Tesi: "Antibacterial mechanism"

1

Ooi, Nicola Chooi Twan. "Antibacterial activity and mechanism of action of lipophilic antioxidants". Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/5905/.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

The emergence and spread of antibiotic resistance hampers effective treatment of bacterial infections. This is particularly the case for infections involving a biofilm component, as the activity of existing antibacterial drugs against these surface-attached communities is limited. The work presented in this thesis sought to identify and characterise compounds with antibacterial and antibiofilm activity against the important pathogen, Staphylococcus aureus. Antistaphylococcal activity was assessed for 16 antioxidants that are used in cosmetics, traditional medicines or as food additives, and which have been reported previously to have some antibacterial activity. Initial experiments with tert-butylhydroquinone (TBHQ) showed that activity that had previously been ascribed to the antioxidant, was a consequence of its conversion to tert-butylbenzoquinone (TBBQ) under culture conditions. TBBQ displayed innate bactericidal activity against S. aureus that was effected through perturbation of the bacterial membrane. The other antioxidants also inhibited staphylococcal growth through perturbation of the cytoplasmic membrane, and compounds that displayed selective action against bacterial membranes were identified. Of the agents with bacterial specificity, TBBQ, celastrol and nordihydroguaiaretic acid (NDGA) also eradicated staphylococcal biofilms; a rare property amongst antibacterial agents. Although these antioxidants exhibited a similar membrane-damaging mode of action, their mechanisms of antibiofilm activity differed. TBBQ eradicated preformed biofilms through sterilisation of slow-growing and persister cell populations, whilst celastrol and NDGA caused physical disruption of the biofilm. All three antioxidants acted synergistically with gentamicin against biofilms, eradicating surface attached populations at concentrations that did not cause irritation or visible damage to a human skin equivalent. The potent and selective antibacterial activity, and low resistance potential upon extended subculture, suggest that these compounds could be used topically in combination with gentamicin to treat infected wounds.

2

Martin, Constance Jean. "Efferocytosis is an Innate Antibacterial Mechanism of Mycobacterium tuberculosis Control". Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10094.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

One third of the world’s population is infected with Mycobacterium tuberculosis, causing two million deaths annually. The bacteria avoid immune clearance by persisting within macrophages by subverting normal phagosome maturation and acidification. In order to spread, the bacteria induce necrotic death of its host macrophage, broadcasting the infection into neighboring cells. However, it has long been appreciated that the apoptotic, rather than necrotic death of an infected macrophage results in bacterial growth suppression, improved adaptive immune response and survival. The mechanism for apoptosis-mediated bacterial suppression has hitherto remained unknown. In this dissertation we report that apoptosis itself is not intrinsically bactericidal. We find that following apoptosis, the M. tuberculosis-infected macrophage is engulfed by bystander macrophages through the process of efferocytosis. Efferocytosis, or apoptotic cell clearance, is a critical function of macrophages; however, little is known regarding efferocytosis of infected apoptotic cells. We find that M. tuberculosis-infected macrophages die by apoptosis more commonly than found previously. By confocal microscopy we observed that apoptotic macrophages are rapidly engulfed by uninfected macrophages. Efferocytosis of M. tuberculosisinfected macrophages occurs in vitro with all macrophage types tested and in vivo- specifically in the lung, indicating that efferocytosis could play an important role during infection. We developed an uninfected macrophage co-culture system in which we observe efferocytosis and define conditions in which it occurs. Using this co-culture system we observe a suppression of bacterial growth. By blocking efferocytosis, we have found that the engulfment of infected cells is required for M. tuberculosis control in the macrophage co-culture system, demonstrating that efferocytosis is a novel antibacterial mechanism. We then demonstrated using transmission electron microscopy that the M. tuberculosis-containing efferocytic phagosome is structurally distinct from the traditional M. tuberculosis phagosome. Bacteria from within the efferocytic phagosome are unable to halt its maturation, and as such are delivered to lysosomes. Furthermore, we find that following efferocytosis, M. tuberculosis are killed. While efferocytosis is recognized as a constitutive housekeeping function of macrophages, our work indicates that is should also be viewed as an antimicrobial effector mechanism.

3

Adeyemi, Temitope. "Investigating the mechanism of action of potato extract against Helicobacter pylori". Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/investigating-the-mechanism-of-action-of-potato-extract-against-helicobacter-pylori(ddc5d0b6-6cbf-45aa-98ec-408de595e3f4).html.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Helicobacter pylori is a Gram-negative bacterium that is the major cause of many upper gastrointestinal diseases such as gastritis and peptic ulcer disease. It has the unique ability of colonising the human gastric mucosa. Failure in complete eradication of H. pylori in infected patients, mainly due to antibiotic resistance, has necessitated the development of better therapeutics, especially from natural sources. In this study, extract of Maris piper potatoes were obtained and evaluated for antibacterial activity against H. pylori in vitro. Antibacterial activity was carried out against antibiotic-sensitive and clinical antibiotic-resistant H. pylori strains, as well as a range of Gram-negative bacteria including Helicobacter and Campylobacter species, using the viable count method. Result of the antibacterial assays indicated that potato extract is bactericidal against H. pylori lab strain as well as clinical antibiotic-resistant strains, with minimum inhibitory concentration at 15.6 mg/ml. Potato extract also showed minimal antibacterial activity against other Gram- negative bacteria tested, with minimum inhibitory concentration at 250 mg/ml. The effect of the extract on the morphology of H. pylori was also observed by transmission electron microscopy (TEM). TEM analysis of potato extract-treated H. pylori cells showed disruption of the morphology of H. pylori, characterized by separation of the outer membrane from the inner membrane and loss of cell shape. Potato extract also caused hyperpolarisation of H. pylori plasma membrane; however it is unclear whether the membrane active pumping activity is affected. Mutants of H. pylori that are resistant to potato extract were generated as a means to identify the target of potato extract within the H. pylori genome. Genome sequence analysis led to the discovery of a hypothetical protein, encoded by HP0603 gene, which may be involved in inducing resistance to potato extract. The results obtained in this study provide great insights into the anti-H. pylori activity of potato extract. Overall, this study suggests the potential use of potato extract as a source of anti-H. pylori agents; and stimulates further studies into identifying its mechanism of action.

4

Silva, Fernanda Dias da. "Mecanismo de ação da microplusina, um peptídeo quelante de cobre com atividade antimicrobiana". Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/42/42135/tde-02122008-180144/.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Peptídeos antimicrobianos (PAMs) fazem parte de um dos mecanismos da imunidade inata contra infecções. A microplusina é um PAM de 10.204 Da, isolado da hemolinfa livre de células e dos ovos do carrapato Rhipicephalus (Boophilus) microplus. É um PAM aniônico em pH fisiológico, possui seis resíduos de cisteína, com formação de três pontes dissulfeto, além de sete resíduos de histidina concentrados principalmente na sua porção C-terminal. O presente trabalho teve como objetivo investigar o mecanismo de ação antimicrobiana da microplusina. A microplusina recombinante é ativa contra várias bactérias Gram-positivas e fungos, porém não apresenta atividade contra bactérias Gram-negativas. Para avaliar o seu mecanismo de ação, foram utilizados dois modelos: a bactéria Micrococcus luteus e o fungo Cryptococcus neoformans. A microplusina é bacteriostática contra M. luteus e apresenta localização intracelular na bactéria. Além disso, observamos que a microplusina liga cobre e que a adição deste metal ao meio de cultivo reduz sua atividade antibacteriana. Bactérias M. luteus pré-incubadas com microplusina retomam o seu crescimento quando cobre é adicionado ao meio. Estes dados indicam que a atividade da microplusina está relacionada à sua habilidade de depletar cobre do meio extra ou intracelular, sugerindo um efeito nutricional para o peptídeo. A microplusina apresenta estrutura terciária com cinco a-hélices e sua ligação ao cobre não induz mudanças conformacionais. Observou-se que as histidinas 1, 2 e 74 da microplusina podem estar envolvidas na formação de um sítio de ligação ao cobre. Quanto à C. neoformans, verificou-se que a microplusina inibe a melanização do fungo, um fator de virulência catalisado pela lacase, uma enzima cobre-dependente. Entretanto, a microplusina não afeta a atividade da lacase, nem sua expressão gênica. O peptídeo também não inibe a auto-polimerização de substratos fenólicos que levam à melanização. Sendo assim, mais estudos são necessários a fim de avaliar o mecanismo pelo qual a microplusina inibe a melanização. Adicionalmente, a microplusina afeta a viabilidade do fungo e reduz o tamanho de sua cápsula, outro importante fator de virulência. As atividades da microplusina sobre C. neoformans sugerem o seu potencial terapêutico. Experimentos in vivo com modelo murino, mostraram que a microplusina reduz o processo inflamatório e a viabilidade de C. neoformans nos pulmões, indicando que em condições otimizadas, o peptídeo pode atuar no controle de infecções.
Antimicrobial peptides (AMPs) take part of innate immune mechanisms against infections. Microplusin is a 10,204 Da AMP, isolated from cell-free hemolymph and eggs of the tick Rhipicephalus (Boophilus) microplus. It is an anionic AMP at physiological pH, with six cysteine residues forming three disulfide bridges and seven histidine residues clustered mainly at the carboxy end portion. The goal of the present work was investigate the antimicrobial action mechanism of microplusin. Recombinant microplusin is active against Gram-positive bacteria and fungi, however, no activity is detected for Gram-negative bacteria. Two models were used to evaluate the action mechanism of microplusin: the bacteria Micrococcus luteus and the yeast Cryptococcus neoformans. Microplusin is bacteriostatic against M. luteus and its localization is intracellular for these bacteria. Moreover, microplusin binds copper and the addition of this metal into the medium reduces its antibacterial activity. M. luteus bacteria pre-treated with microplusin recover its growth when copper is added. These data indicate that microplusin activity is related to its ability to deplete copper present in the extracellular or intracellular environment, suggesting a nutritional effect. Microplusin presents a tertiary structure with five a-helix and the copper binding does not induce conformation changes. In addition, it was observed that histidines 1, 2 and 74 from microplusin may be involved in the formation of a copper binding site. About C. neoformans, it was verified microplusin inhibits its melanization, a virulence factor catalyzed by laccase, a copper dependent enzyme. However, microplusin does affect neither laccase activity nor its gene expression. The melanization caused by auto-polymerazation of phenolic substrates, is also not inhibited by microplusin. Hence, additional studies are required to evaluate the mechanism by which microplusin inhibits melanization. In addition, microplusin also affects the fungi viability and reduces the capsule size, another important virulence factor.The microplusin activities against C. neoformans suggest its therapeutic potential. In vivo experiments with murine model showed that microplusin reduces the inflammation and the viability of C. neoformans in the lungs, indicating that, in optimized conditions, the peptide may act in the infection control.

5

Dannenberg, Guilherme da Silva. "Óleo essencial de pimenta rosa (Schinus terebinthifolius RADDI): atividade antimicrobiana e aplicação como componente ativo em filme para bioconservação de alimentos". Universidade Federal de Pelotas, 2017. http://repositorio.ufpel.edu.br:8080/handle/prefix/3666.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Submitted by Gabriela Lopes (gmachadolopesufpel@gmail.com) on 2017-07-07T15:23:04Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) TESE - Dannenberg 2017.pdf: 1125673 bytes, checksum: 659297f040c56e3fca1291a9ee608e18 (MD5)
Approved for entry into archive by Aline Batista (alinehb.ufpel@gmail.com) on 2017-07-17T19:55:10Z (GMT) No. of bitstreams: 2 TESE - Dannenberg 2017.pdf: 1125673 bytes, checksum: 659297f040c56e3fca1291a9ee608e18 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Made available in DSpace on 2017-07-17T19:55:10Z (GMT). No. of bitstreams: 2 TESE - Dannenberg 2017.pdf: 1125673 bytes, checksum: 659297f040c56e3fca1291a9ee608e18 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-05-30
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
A utilização de conservantes naturais bem como de embalagens ativas vêm ganhando espaço na indústria de alimentos. Neste trabalho, objetivou-se avaliar as características antimicrobianas do óleo essencial de pimenta rosa (OEPR) e, utilizá- lo como componente ativo na elaboração de filmes para aplicação no desenvolvimento de embalagens bioconservantes para alimentos. Através da análise cromatográfica (CG/MS), detectou-se 18 compostos, 4 monoterpenos e 14 sesquiterpenos, dos quais β-mirceno (41%), β-cuvebeno (12%) e Limoneno (9%) foram os majoritários. Na atividade antimicrobiana do OEPR em ágar e caldo, verificou-se ação contra cinco bactérias patogênicas. A CIM (Concentração Inibitória Mínima) para S. aureus e L. monocytogenes foi de 0,68 e 1,36 mg/mL, respectivamente e a CBM (Concentração Bactericida Mínima) foi de 2,72 mg/mL, para ambas. Em micro-atmosfera a redução foi de 100% no desenvolvimento de S. aureus e L. monocytogenes e, 16 e 15% para E. coli e S. Typhimurium. O tempo de contato necessário para a CBM agir sobre bactérias Gram positivas foi inferior ao período de 12 h, e bactérias Gram negativas não foram inibidas. Além disso, foram verificadas alterações na permeabilidade e integridade da membrana citoplasmática de todas as bactérias avaliadas, indicando que o dano no envoltório celular é um dos seus mecanismos de ação. O OEPR foi aplicado como componente ativo em filmes de acetato de celulose, avaliados in vitro (ágar, caldo e micro-atmosfera) e in situ (queijo mozarela fatiado) contra bactérias patogênicas. Foi verificado que concentrações de 2, 4 e 6% de OEPR na matriz polimérica, conferiu atividade em todos os meios avaliados contra L. monocytogenes e S. aureus. Escherichia coli foi sensível em meio liquido e em micro-atmosfera, enquanto S. Typhimurium não demonstrou sensibilidade aos filmes antibacterianos. A inibição in situ, demonstrou que a afinidade entre as moléculas apolares do OEPR e os componentes lipídicos do queijo permite a migração do OE do interior do polímero para a superfície facilitando sua dispersão no alimento, indicando favorável sua aplicação como embalagem ativa.
The use of natural preservatives as well as active packaging has sparked interest in the food industry. The objective of this work was to evaluate the antimicrobial characteristics of the essential oil of pink pepper (PPEO) and to use it as an active component in the elaboration of films for application in the development of bioconservant packaging for food. Through the chromatographic analysis (GC/MS) 18 compounds, 4 monoterpenes and 14 sesquiterpenes were detected, of which β- myrcene (41%), β-cuvebene (12%) and Limonene (9%) were the majority. In the antimicrobial activity of PPEO in agar and broth, action was observed against five pathogenic bacteria. The MIC for S. aureus and L. monocytogenes was 0.68 and 1.36 mg/mL, and the MBC was 2.72 mg/mL for both. In micro-atmosphere the reduction was 100% in the development of S. aureus and L. monocytogenes, and 16 and 15% for E. coli and S. Typhimurium. The contact time required for MBC to act on Gram positive bacteria was lower than the 12 h period, and Gram negative bacteria were not inhibited. In addition, changes in the permeability and integrity of the cytoplasmic membrane of all evaluated bacteria were observed, indicating that damage in the cellular envelope is one of its mechanisms of action. PPEO was applied as an active component in cellulose acetate films evaluated in vitro (agar, broth and micro-atmosphere) and in situ (sliced mozzarella cheese) against pathogenic bacteria. It was found that concentrations of 2, 4 and 6% PPEO in the polymer matrix conferred activity on all média evaluated against L. monocytogenes and S. aureus. Escherichia coli was sensitive in liquid medium and in microatmosphere, while S. Typhimurium showed no sensitivity to antibacterial films. In situ inhibition has demonstrated that the affinity between the OEPR apolar molecules and the lipid components of the cheese allows migration of the OE from the interior of the polymer to the surface and facilitates its dispersion in the food, indicating its favorable application as an active packaging. Keywords: Essential oil; Antibacterial activity;

6

Jacry, Cécile. "Découverte de nouvelles molécules antibiotiques et caractérisation de leurs modes d'action". Thesis, université Paris-Saclay, 2021. http://www.theses.fr/2021UPASL009.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Les flavonoïdes sont des métabolites secondaires largement répandus chez les plantes et appartiennent à une grande famille de composés chimiques d'intérêt industriel. Les flavonoïdes sont une source importante de nouveaux médicaments et nutraceutiques en raison de leurs activités anti-oxydantes, antivirales, antimicrobiennes, anticancéreuses, etc. Notre étude se concentre sur la caractérisation de l'activité antibactérienne des flavonoïdes ciblant spécifiquement les bactéries à Gram positif. Les objectifs de mon travail de recherche sont i) de mettre en place des méthodologies de cribles efficaces et rapides afin d’évaluer l’activité antibactérienne des flavonoïdes et ii) de déterminer les mécanismes d'action antibactérien des flavonoïdes. La caractérisation de l'activité antibactérienne des flavonoïdes a été réalisée avec des tests de toxicité des flavonoïdes envers la bactérie modèle à Gram positif B. subtilis par la méthode du Live Cell Array permettant d'enregistrer la cinétique de croissance bactérienne en temps réel. Différentes stratégies ont été employées pour décrypter le(s) mode(s) d'action des flavonoïdes ; telles que le crible d'une banque de flavonoïdes pour l'identification de nouveaux composés actifs contre B. subtilis, le crible d'une collection de mutants de B. subtilis pour l'identification de gènes impliqués dans la réponse de B. subtilis aux flavonoïdes, une évolution dirigée en laboratoire de B. subtilis en présence de flavonoïde pour l'obtention et la caractérisation de souches résistantes aux flavonoïdes, et enfin une analyse de la réponse transcriptionnelle de B. subtilis en présence de flavonoïdes. Deux flavonoïdes déjà identifiés dans la littérature pour inhiber la croissance de bactéries à Gram positif, la pinocembrine et la naringénine, ont une activité antibactérienne contre B. subtilis. Une diminution de 50 % du taux de croissance a été observée en présence de 93 mg.L ⁻¹ ou 32 mg.L ⁻¹ de naringénine ou pinocembrine respectivement.Pour décrypter les mécanismes d'action des flavonoïdes, une collection de 63 flavonoïdes a été criblée et les concentrations minimales inhibitrices (MICs) déterminées pour chaque flavonoïde en présence de B. subtilis. 17 flavonoïdes se sont avérés particulièrement actifs contre B. subtilis. La tentative d'établir un modèle QSAR (relation quantitative structure-activité) avec les 17 flavonoïdes actifs n'a malheureusement pas été concluante car malgré l'obtention d'une régression linéaire largement acceptable (R²≈ 0,9), la validation par exclusion systématique d'un composé ("leave one out") n'a pas été obtenue. La seule explication plausible de cet échec est que le nombre de modes d'action présents est trop élevé pour un set de 17 composés, rendant ainsi caduque la modélisation QSAR. Au cours d'un crible de 67 mutants de B. subtilis, huit gènes impliqués dans la réponse aux flavonoïdes (naringénine et pinocembrine) ont été identifiés, dont deux appartiennent au régulon LmrA/QdoR, déjà identifié dans la littérature pour répondre aux flavonoïdes. Les souches B. subtilis ∆lmrA et ∆qdoI sont respectivement plus sensibles et plus résistantes vis-à-vis de la naringénine et de la pinocembrine. Les 17 flavonoïdes précédemment identifiés et actifs envers B. subtilis induisent une réponse transcriptionnelle propre à chacun d'après notre analyse de l'activité de 10 promoteurs avec l'utilisation de fusions transcriptionnelles avec un gène rapporteur. Cette analyse est cohérente avec l'étude transcriptomique menée pour la caractérisation de la réponse de B. subtilis en présence de 5 flavonoïdes ; la 2’hydroxyflavanone, la bavachine, la naringénine, la pinocembrine et le résokaempférol. De ce travail ressort plusieurs modes d'action des flavonoïdes chez B. subtilis, impliquant l'induction de la réponse stringente, l'inhibition de voies métaboliques pour la synthèse des membranes et paroi cellulaires et l'inhibition du métabolisme carboné central
Flavonoids are secondary metabolites widespread in plants and belong to a large family of chemical compounds of industrial interest. Flavonoids are an important source of new drugs and nutraceuticals because of their antioxidant, antiviral, antimicrobial, anticancer activities. Our study focuses on the characterization of the antibacterial activity of flavonoids specifically targeting Gram-positive bacteria. The objectives of my research work are i) to establish efficient and rapid screening methodologies to evaluate the antibacterial activity of flavonoids and ii) to determine the mechanisms of action of antibacterial flavonoids. The characterization of the antibacterial activity of flavonoids was carried out with flavonoid toxicity tests against the Gram-positive model bacterium B. subtilis by Live Cell Array method, which measures the bacterial growth kinetics. Several strategies were used to decipher the mode(s) of action of the flavonoids, such as screening a flavonoid library for new compounds active against B. subtilis, screening a collection of B. subtilis mutants for the identification of genes involved in the flavonoid response of B. subtilis, an adaptive laboratory evolution of B. subtilis in presence of flavonoid to obtain and characterize flavonoid-resistant strains, and finally an analysis of the transcriptional response of B. subtilis in the presence of flavonoids. Two flavonoids already identified in the literature to inhibit the growth of Gram-positive bacteria, pinocembrin and naringenin, have antibacterial activity against B. subtilis. A 50% decrease in growth rate was observed in the presence of 93 mg.L ⁻¹ or 32 mg.L ⁻¹ of naringenin or pinocembrin respectively.To decipher the mechanisms of action of the flavonoids, a collection of 63 flavonoids was screened and minimal inhibitory concentrations (MICs) were determined for each flavonoid in the presence of B. subtilis. 17 flavonoids were found to be particularly active against B. subtilis. The attempt to establish a QSAR (quantitative structure activity relationship) model with the 17 active flavonoids was unfortunately not conclusive because, despite obtaining a high quality linear regression (R² ≈ 0.9), cross-validation by using leave-one-out basic method was not obtained. The only plausible explanation for this failure is that the number of modes of action present is too high for a set of 17 compounds, thus rendering the QSAR model obsolete. In a screen of 67 mutants of B. subtilis, eight genes involved in the response to flavonoids (naringenin and pinocembrin) were identified, two of which belong to the LmrA/QdoR regulon, already identified in the literature to respond to flavonoids. The B. subtilis strains ∆lmrA and ∆qdoI are respectively more sensitive and more resistant to naringenin and pinocembrin. The 17 flavonoids previously identified and active against B. subtilis induce a flavonoid-specific transcriptional response according to our analysis of the activity of 10 promoters with the use of transcriptional fusions with a reporter gene. This analysis is consistent with the transcriptomic study carried out for the characterization of the response of B. subtilis in the presence of 5 flavonoids; 2'hydroxyflavanone, bavachine, naringenin, pinocembrin and resokaempferol. Several modes of action of the flavonoids in B. subtilis were identified, involving induction of the stringent response, inhibition of metabolic pathways for cell membrane and cell wall synthesis, and inhibition of central carbon metabolism

7

Bouhallab, Saïd. "Mecanisme d'action des facteurs i et ii des pristinamycines : etude de leur synergie et localisation du site de fixation de la pristinamycine ia". Paris 6, 1988. http://www.theses.fr/1988PA066095.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

8

Brunel, Frédéric. "Synthèse, conception et élaboration de nouveaux systèmes dérivés de liquides ioniques antibactériens à base de phosphonium". Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4087.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Un récent rapport de l’OMS met en garde les autorités de santé sur l’émergence de résistances chez les bactéries et le développement de souches bactériennes multi-résistantes aux traitements antibiotiques actuels. La progression de ces phénomènes est dû à différents facteurs. L’environnement hospitalier concentre un usage important de traitements antibiotiques et représente ainsi un terreau favorable au développement de résistances chez les bactéries. Le staphylocoque doré, ainsi que sa souche résistante (SARM), s’avèrent problématiques et entraînent un grand nombre de maladies nosocomiales. Dans ce contexte, il est primordial de mettre au point de nouveaux agents antibactériens permettant de lutter contre ces bactéries. Les liquides ioniques (sels à point de fusion bas) démontrent d’importantes propriétés antibactériennes. Néanmoins les mécanismes de cet effet bactéricide n’ont pas encore été établis. Ainsi nous nous proposons, dans un premier temps, de synthétiser des liquides ioniques di-cationiques afin d’étudier les différents facteurs structuraux qui régissent leur activité antibactérienne. Dans un second temps, nous concevrons des liquides ioniques à base de phosphoniums fonctionnalisés avec une sonde fluorescente. En exploitant les propriétés spectroscopiques, nous tenterons d’observer leurs interactions avec les cellules bactériennes. Enfin, nous nous proposons d'utiliser les phosphoniums comme agents de fonctionnalisation de surface dans le but de mettre au point des surfaces aux qualités bactéricides intrinsèques. Pour ce faire nous utiliserons différentes méthodes comme la conception de monocouches auto-assemblées ou l’électropolymérisation
A recent WHO report warns the health authorities about the emergence of new bacterial resistances and the development of multi-resistant strains against current antibiotics treatments. The growth of those resistances is due to several factors. The hospital environment concentrates a significant use of antibiotics and disinfectant representing a favorable ground for bacterial resistance development. Among them the Staphylococcus aureus and its methicillin resistant strain (MRSA) represent a crucial issue in care environments and is a major cause of hospital acquired infections. In this context, it is essential to develop new antibacterial agents to fight against these bacteria. Ionic liquid are low melting point salts, they show significant antibacterial properties. However, the fact that the mechanisms of action of their bactericidal effect have not been established yet constitutes a major obstacle to their development as bactericidal agents. Thus, we propose to synthetize ammonium- and phosphonium-based di-cationic ionic liquids in order to study the different structural factors that govern their antibacterial activity. Then we will develop phosphonium based ionic liquids functionalized with a fluorescent probe. By taking advantage of their spectroscopic properties we will try to observe their interactions with bacterial cells. Finally, we propose to use the phosphonium salts as surface functionalization agents in order to design surfaces with intrinsic antibacterial properties. To do so, we will use innovative methods such as conception of self-assembled monolayers or electropolymerization technics

9

Moore, Suzanne Louise. "The mechanisms of antibacterial action of some nonionic surfactants". Thesis, University of Brighton, 1997. https://research.brighton.ac.uk/en/studentTheses/35414631-9ae5-4dc4-afd4-6f724fe9a7f6.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Antibacterial agents are composed of a diverse group and many such agents have entered common usage through experience with little information on their mechanism of action. Study of the mechanism of action of an antimicrobial agent provides an insight into resistance mechanisms, toxicological problems and the design and development of new agents or combinations. The primary target of most antimicrobial agents (excluding antibiotics) is the cytoplasmic membrane and associated enzymes. Membrane-active agents can cause a change in the fluidity and/or permeability of the cytoplasmic membrane. Such changes can be determined by the leakage of cellular constituents such as potassium ions, nucleotides and their constituents and amino acids. The effect of an anti bacterial agent on the cytoplasmic membrane can also be determined by elucidating the effect of the antibacterial agent on the activity of membrane-bound enzymes and substrate uptake.

10

Zhang, Huichun. "Metal oxide-facilitated oxidation of antibacterial agents". Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-07072004-152317/unrestricted/zhang%5Fhuichun%5F200407%5Fphd.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Thesis (Ph. D.)--School of Civil and Environmental Engineering, Georgia Institute of Technology, 2005. Directed by Ching-Hua Huang.
Wine, Paul, Committee Member ; Pavlostathis, Spyros, Committee Member ; Mulholland, James, Committee Member ; Yiacoumi, Sotira, Committee Member ; Huang, Ching-Hua, Committee Chair. Includes bibliographical references.

11

Brunel, Frédéric. "Synthèse, conception et élaboration de nouveaux systèmes dérivés de liquides ioniques antibactériens à base de phosphonium". Electronic Thesis or Diss., Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4087.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Un récent rapport de l’OMS met en garde les autorités de santé sur l’émergence de résistances chez les bactéries et le développement de souches bactériennes multi-résistantes aux traitements antibiotiques actuels. La progression de ces phénomènes est dû à différents facteurs. L’environnement hospitalier concentre un usage important de traitements antibiotiques et représente ainsi un terreau favorable au développement de résistances chez les bactéries. Le staphylocoque doré, ainsi que sa souche résistante (SARM), s’avèrent problématiques et entraînent un grand nombre de maladies nosocomiales. Dans ce contexte, il est primordial de mettre au point de nouveaux agents antibactériens permettant de lutter contre ces bactéries. Les liquides ioniques (sels à point de fusion bas) démontrent d’importantes propriétés antibactériennes. Néanmoins les mécanismes de cet effet bactéricide n’ont pas encore été établis. Ainsi nous nous proposons, dans un premier temps, de synthétiser des liquides ioniques di-cationiques afin d’étudier les différents facteurs structuraux qui régissent leur activité antibactérienne. Dans un second temps, nous concevrons des liquides ioniques à base de phosphoniums fonctionnalisés avec une sonde fluorescente. En exploitant les propriétés spectroscopiques, nous tenterons d’observer leurs interactions avec les cellules bactériennes. Enfin, nous nous proposons d'utiliser les phosphoniums comme agents de fonctionnalisation de surface dans le but de mettre au point des surfaces aux qualités bactéricides intrinsèques. Pour ce faire nous utiliserons différentes méthodes comme la conception de monocouches auto-assemblées ou l’électropolymérisation
A recent WHO report warns the health authorities about the emergence of new bacterial resistances and the development of multi-resistant strains against current antibiotics treatments. The growth of those resistances is due to several factors. The hospital environment concentrates a significant use of antibiotics and disinfectant representing a favorable ground for bacterial resistance development. Among them the Staphylococcus aureus and its methicillin resistant strain (MRSA) represent a crucial issue in care environments and is a major cause of hospital acquired infections. In this context, it is essential to develop new antibacterial agents to fight against these bacteria. Ionic liquid are low melting point salts, they show significant antibacterial properties. However, the fact that the mechanisms of action of their bactericidal effect have not been established yet constitutes a major obstacle to their development as bactericidal agents. Thus, we propose to synthetize ammonium- and phosphonium-based di-cationic ionic liquids in order to study the different structural factors that govern their antibacterial activity. Then we will develop phosphonium based ionic liquids functionalized with a fluorescent probe. By taking advantage of their spectroscopic properties we will try to observe their interactions with bacterial cells. Finally, we propose to use the phosphonium salts as surface functionalization agents in order to design surfaces with intrinsic antibacterial properties. To do so, we will use innovative methods such as conception of self-assembled monolayers or electropolymerization technics

12

Randall, Christopher Paul. "The silver cation (Ag+) : antibacterial mode of action and mechanisms of resistance". Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/5915/.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

The increasing prevalence of infections attributed to antibiotic-resistant bacteria has prompted renewed interest in exploiting the antibacterial properties of Ag+ to treat such infections. However, the antibacterial mode of action (MOA) and bactericidal activity of Ag+ are poorly understood, and there are concerns that the prolific and unrestricted use of Ag+ in consumer products will select bacterial Ag+ resistance, thus limiting the clinical utility of Ag+. Ag+ resistance already exists, although aspects of the molecular basis of Ag+ resistance, and the current prevalence of Ag+-resistant pathogens are unclear. This thesis sought to address these issues. Ag+ was found to be bacteriostatic in culture media and bactericidal in buffer, and was unable to eradicate Staphylococcus aureus biofilms in vitro. MOA studies indicated that the primary antibacterial target of Ag+ is the cell membrane. Evidence was obtained suggesting that Ag+ does not interfere with the phospholipid component of the membrane, but instead probably damages integral membrane proteins to produce an antibacterial effect. A survey of hospital staphylococcal isolates (n=1006) found universal susceptibility to Ag+, and Ag+ resistance could not be selected in S. aureus and several other pathogens in vitro. However, in Escherichia coli, high-level Ag+ resistance arose rapidly and was not associated with a fitness cost likely to prevent its emergence in the clinical setting. Ag+-resistant strains contained mutations in genes regulating expression of an Ag+ efflux mechanism and outer membrane porins. A detailed characterisation of a known Ag+-resistance determinant (the sil operon), was also conducted to provide further insights into the mechanism of Ag+ resistance conferred by this determinant. Collectively, these studies provide further insights into the MOA of Ag+ and the mechanisms of Ag+ resistance, which could potentially be applied to optimising the future uses of Ag+ as an antibacterial agent.

13

Chawner, J. A. "A comparative study of the mechanisms of action of alexidine and chlorhexidine against Escherichia coli ATCC 8739". Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233091.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

14

Julien, Louis. "Understanding the relationship between antibacterial activity and iron-restriction mechanisms in egg-white". Thesis, Rennes, Agrocampus Ouest, 2020. http://www.theses.fr/2020NSARB339.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Salmonella Enteritidis est le pathogène le plus fréquemment identifié dans les œufs et ovoproduits au sein de l’Union Européene. Pour coloniser les œufs, S. Enteritidis doit surmonter de nombreux obstacles liés à l’activité antibactérienne du blanc d'œuf (BO). Un des mécanismes antibactériens majeurs du BO est la restriction en fer imposée par l'ovotransferrine (protéine liant le fer ferrique, Fe3+). Pour pallier cette carence, S. Enteritidis est capable de synthétiser deux types de sidérophores, l’entérobactine et la salmochéline, capables d’acquérir le fer des protéines de l'hôte. Cependant, le BO contient également une protéine de type lipocaline (Ex-FABP) connue pour séquestrer l’entérobactine. Deux autres lipocalines, Cal-¿ et l’a1-ovoglycoprotéine ont été identifiées dans le BO, mais leur capacité à séquestrer des sidérophores restait à explorer.L'objectif de ce projet était d'étudier l’activité antimicrobienne de trois lipocalines du BO par leur capacité à séquestrer les deux sidérophores de S. Enteritidis. Les résultats montrent que Cal-¿ et l’a1-ovoglycoprotéine ne sequestrent ni l’entérobactine ni la salmochéline. Nos observations confirment qu’Ex-FABP lie uniquement l’entérobactine et non la salmochéline. En milieux de culture, S. Enteritidis échappe à l'inhibition de croissance induite par Ex-FABP grâce à la synthèse de salmochéline. Néanmoins, le rôle antimicrobien d’Ex-FABP via la séquestration de sidérophores n’a pas été observé dans le BO. Ceci pourrait être lié à la faible croissance de S. Enteritidis dans le BO et au fait que les sidérophores ne semblent pas être nécessaires à sa survie dans ce milieu
Salmonella Enteritidis is the most prevalent food-borne pathogen associated with egg-related outbreaks in the European Union. In order to colonise eggs, S. Enteritidis must resist the powerful anti-bacterial activities of egg white (EW). Possibly, the major EW antibacterial property is iron restriction, which results from the presence of the Fe3+-binding protein, ovotransferrin. To circumvent iron restriction, S. Enteritidis synthesise two types of catecholate siderophores, enterobactin and salmochelin, that can chelate iron from host iron-binding proteins. However, EW contains a lipocalin (Ex-FABP) that is known to bind enterobactin. Two other lipocalins, Cal-¿ and a1-ovoglycoprotein, are found in EW but their siderophore-binding potential was yet to be exploredThe aim of this project was to study the antimicrobial activity of three EW lipocalins through sequestration of bacterial siderophores synthesised by S. Enteritidis. Among those lipocalins, Cal-¿ and a1-ovoglycoprotein were shown to bind neither enterobactin nor salmochelin. Further, it was confirmed that Ex-FABP binds only enterobactin and not salmochelin. In standard growth media, S. Enteritidis escaped Ex-FABP-mediated growth inhibition thanks to salmochelin synthesis. However, no clear antibacterial activity was observed for Ex-FABP in EW. This surprising observation might be correlated with the weak growth of S. Enteritidis in EW and a lack of requirement for siderophores in persistence

15

Boberek, Jaroslaw M. "The mechanisms of action of the plant-derived antibacterials berberine and falcarindiol". Thesis, Royal Veterinary College (University of London), 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.572449.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

16

Kamali-Moghaddam, Masood. "Co-operative recombination mechanisms promoting gene clustering and lateral transfer of antibacterial drug resistance". Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2001. http://publications.uu.se/theses/91-554-4936-0/.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

17

Wigle, Tim J. Singleton Scott F. "The evolution of antibacterial chemotherapy targeting RecA to sabotage antibiotic tolerance and resistance mechanisms /". Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2007. http://dc.lib.unc.edu/u?/etd,1493.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2008.
Title from electronic title page (viewed Sep. 16, 2008). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the School of Pharmacy." Discipline: Pharmacy; Department/School: Pharmacy.

18

Jesse, Helen. "Carbon monoxide and carbon monoxide-releasing molecules as novel antibacterial agents : mechanisms of toxicity and resistance". Thesis, University of Sheffield, 2012. http://etheses.whiterose.ac.uk/4809/.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Carbon monoxide (CO) is commonly considered to be toxic due to the propensity of this gaseous molecule to bind to ferrous iron in haemoglobin and cytochromes, thereby inhibiting respiration and the transport of oxygen around the body. However, CO is produced endogenously by haem oxygenases and has various cytoprotective functions including being vasodilatory, anti-inflammatory and anti-apoptotic. The development of CO-RMs (Carbon Monoxide-Releasing Molecules), which are generally transition metal carbonyls that release CO under certain conditions, has facilitated research into the physiological effects of CO and the potential use of CO as a therapeutic agent. Furthermore, CO-RMs have been found to reduce significantly the viability of various Gram-positive and Gram-negative bacteria, which is thought to be caused in part by the binding of CO from CO-RMs to the terminal oxidases of aerobic respiratory chains. Interestingly, CO-RMs are known to elicit many effects distinct from those of CO gas, including acting as more potent bactericidal agents. This thesis aims to increase the current knowledge of the antibacterial effects of CORMs, with a particular focus on the interactions with respiration, oxidases and thiol compounds. In contrast to CO gas, CORM-3 was not preferentially inhibitory to respiration at low oxygen tensions; however, in accordance with the relative resistance of cytochrome bd-I to CO gas, this oxidase was found to be the most resistant of E. coli to respiratory inhibition by CORM-3, and possession of this oxidase conferred some protection against growth inhibition in the presence of this CO-RM. Inhibition of E. coli respiration by CORM-3 was photosensitive and light reduced significantly the toxic effects of this compound, suggesting that CO from CORM-3 binds to ferrous haems in a classical, light-sensitive manner. This supports the hypothesis that the binding of CO from CORM-3 to haemoproteins is largely responsible for killing by these compounds. However, in opposition to this hypothesis, the non-haem oxidase AOX from Vibrio fischeri was found to be hypersensitive to inhibition by CORM-3, but not to CO, emphasising the complex effects of these compounds. Data are presented to show that thiol-containing compounds, which have been widely reported to abolish the biological effects of CO-RMs, substantially reduce the uptake of ruthenium-containing CO-RMs. The generation of reactive oxygen species by CO-RMs is also demonstrated and investigated. Finally, the generation and preliminary characterisation of CO-RM-resistant E. coli mutants is described. This work was done with the aim of revealing previously unappreciated bacterial targets for CO-RMs. Sugar-transporting phosphotransferase systems were identified as a possible means of CO-RM entry into the bacterial cell.

19

Bouarab, Lynda. "Évaluation du potentiel et de voies innovantes de mise en oeuvre de composés phénoliques antimicrobiens d’origine végétale pour la conservation des aliments". Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1084.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Le règne végétal est une ressource renouvelable d'une large gamme de métabolites secondaires biologiquement actifs. Ces travaux de thèse proposent une stratégie multidisciplinaire d'évaluation du potentiel de composés phénoliques antimicrobiens d'origine végétale pour la conservation des aliments. Un criblage de l'activité antimicrobienne in vitro vis-à-vis de 8 souches de la flore pathogène et d'altération des aliments d'une centaine de molécules pures et une soixantaine d'extraits végétaux a d'abord permis de sélectionner les plus actifs. Différents mécanismes d'action vis-à-vis de S. aureus ont pu être mis en évidence par cytométrie de flux couplée à l'utilisation de marqueurs de l'état physiologique des bactéries pour quelques uns des composés actifs sélectionnés. En vue d'une application à de la viande bovine, l'activité antibactérienne des composés phénoliques ou extraits végétaux les plus actifs a été réévaluée dans des milieux de culture plus complexes mimant leur teneur en protéines et en matières grasses. Les résultats de ce criblage et un suivi microbiologique de viande hachée de bœuf avec 1% (m/m) d'extrait ajouté ont permis d'observer que les pertes d'activité antibactérienne observées étaient notamment corrélées aux interactions des composés phénoliques avec les protéines ou les matières grasses. L'incorporation des composés phénoliques ou extraits végétaux dans des matériaux d'emballage en contact alimentaire a constitué la seconde voie de mise en œuvre envisagée. Des films plastiques conservant une activité antibactérienne ont ainsi pu être élaborés par voie fondue
The plant kingdom is a renewable resource of a wide range of biologically active secondary metabolites. This thesis proposes a multidisciplinary strategy for evaluating the potential of plant-derived antimicrobial phenolic compounds for food preservation. A screening of the antimicrobial activity in vitro against 8 strains of foodborne pathogenic and spoilage microorganisms of a hundred pure molecules and about sixty plant extracts allowed to select the most active. Different mechanisms of action with respect to S. aureus could be demonstrated by flow cytometry coupled with the use of probes of the physiological state of the bacteria for some of the selected active compounds. For application to beef, the antibacterial activity of the most active phenolic compounds or plant extracts has been re-evaluated in more complex culture media mimicking their protein and fat content. The results of this screening and a microbiological monitoring of minced beef with 1% (m / m) of added extract made it possible to observe that the observed losses of antibacterial activity were in particular correlated with the interactions of the phenolic compounds with the proteins or fat. Incorporation of phenolic compounds or plant extracts into packaging materials in contact with food constituted was the second proposed route of implementation. Plastic films that retain antibacterial activity have thus been able to be prepared by melting

20

Hennessen, Fabienne [Verfasser]. "Studies on two compound classes from actinobacteria exhibiting new antibacterial mechanisms of action : chelocardins and telomycins / Fabienne Hennessen". Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2018. http://d-nb.info/1215571372/34.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

21

Maurin, Max. "Rôle du pH phagolysosomial dans l'action des antibiotiques sur les bactéries intracellulaires". Paris 7, 1994. http://www.theses.fr/1994PA077067.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

L'absence d'activité d'un antibiotique sur un microorganisme à vie intracellulaire peut correspondre à son incapacité à pénétrer dans la cellule eucaryote, a une localisation subcellulaire différente de celle du microorganisme considéré, ou à une inactivation intracellulaire de l'antibiotique. Nous avons testé l'hypothèse d'une inactivation des antibiotiques dans le milieu phagolysosomial acide, à travers deux modèles de bactéries vivant dans ce compartiment cellulaire ; staphylococcus aureus et coxiella burnetii. Nous avons vérifié dans un premier temps la possibilité d'alcaliniser le ph phagolysosomial par l'utilisation d'agents lysosomotropes. Nous avons ensuite démontré l'effet bactéricide de l'association des agents lysosomotropes aux antibiotiques, alors que ni les agents lysosomotropes ni les antibiotiques n'étaient bactéricides isolement. L'alcalinisation phagolysosomiale est le mécanisme par lequel les agents lysosomotropes ont rétabli l'activité des antibiotiques. Nous avons par ailleurs élaboré un nouveau modèle expérimental d'endocardite à staphylococcus aureus chez le cobaye. Du fait de la méthodologie utilisée, ce modèle est plus proche de l'endocardite sur valve native. Notre but final est de créer un modèle d'endocardite à coxiella burnetii. Ce modèle permettrait notamment de tester in vivo l'activité de l'association des agents lysosomotropes aux antibiotiques.

22

Velic, Amar. "Mechanics of bacterial interaction and geometry enhancement on nanopatterned surfaces". Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/212531/1/Amar_Velic_Thesis.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

This thesis investigated the deformation and resulting antibacterial activity of bacteria on nanopatterned surfaces, to understand how these surfaces elicit their physical killing action and how they can be optimised. Through finite element and experimental investigation, it was demonstrated that nanopatterned surfaces kill bacteria at their tips by delivering lethal deformation which can be enhanced by reducing key nanopattern dimensions. The findings help towards the development of a new generation antimicrobial materials to combat biofilm infection, fomite transmission and emerging resistance.

23

Awassa, Jazia. "Mécanismes antibactériens des hydroxydes doubles lamellaires à base de zinc". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0155.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Les hydroxydes doubles lamellaires (HDL) sont des composés solides constitués par un ensemble de feuilles d'hydroxydes métalliques divalents M(II) et trivalents M(III) entre lesquels s’insèrent des anions et des molécules d’eau. En raison de la flexibilité des HDL en termes de propriétés physico-chimiques, l’étude des différents mécanismes antibactériens qui leurs sont associés présente un intérêt croissant. Ce travail de thèse vise à étudier différentes hypothèses proposées pour explique l'effet antibactérien des hydroxydes doubles lamellaire (HDL) à base de zinc : (1) interactions directes entre la surface des HDL et les parois bactériennes, (2) libération d'ions métalliques divalents en solution depuis les feuillets des HDL, (3) génération d'espèces réactives de l'oxygène (ROS). Lors d’une première étude, une investigation globale a été réalisée pour déterminer les différents paramètres physico-chimiques influençant l'activité antibactérienne des HDLs M(II)Al(III) (M= Zn, Cu, Ni, Co, Mg). L'effet antimicrobien des HDLs contre les bactéries Gram-positives Staphylococcus aureus et Gram-négatives Escherichia coli a été corrélé en premier lieu à la nature du métal divalent, et en second lieu à la quantité d'ions M2+aq libérés dans le milieu de culture. Cet effet était plus prononcé pour les HDLs à base de Zn(II) possédant la plus forte activité antibactérienne et dont les propriétés antibactériennes dépendent du profil de libération des ions Zn2+aq (Mécanisme 2) contrôlée initialement par les différents paramètres physico-chimiques étudiés. De plus, rôle du contact direct (Mécanisme 2) a été validé pour les HDLs à base de Zn(II) en comparant l'activité antibactérienne d’HDLs de taille micrométrique contre S. aureus à celle des nanoparticules (NPs) d’HDL présentant un effet antibactérien supérieur. La présence d'interactions spécifiques entre les HDLs à base de Zn(II) et la paroi de S. aureus a été validée par microscopie à force atomique en mode spectroscopie de force (AFM-FS). L'amélioration des propriétés antibactériennes des NPs d’HDL à base de Zn(II) par la génération de ROS (Mécanisme 3) en présence de lumière UVA a également été évaluée. Après avoir fourni des preuves expérimentales sur les trois mécanismes suggérés, la contribution de chaque mécanisme dans l'activité antibactérienne des HDLs à base de Zn(II) a été déterminé
Layered double hydroxides (LDH) are solid compounds constituted by the stacking of divalent M(II) and trivalent M(III) metal hydroxide sheets separated by an interlayer of anions and water molecules. Due to the versatility of LDH in terms of their tunable physico-chemical properties, a growing interest arises for investigating their different antibacterial activity mechanisms. This thesis work aims at studying the different proposed hypotheses explaining the antibacterial effect of pristine zinc-based LDHs: (1) direct interactions between the surface of LDH and bacterial cell walls, (2) release of constituent divalent metal ions, (3) generation of reactive oxygen species (ROS). First a global investigation was performed to determine the different physico-chemical parameters influencing the antibacterial activity of pristine M(II)Al(III) LDHs (M= Zn, Cu, Ni, Co, Mg). The antimicrobial effect of LDHs against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria was linked in the first place to the nature of divalent metal itself, and to the amount of released M2+aq ions into the culture media in the second place. This effect was more easily identified in Zn(II)-based LDHs possessing the strongest antibacterial activity and whose antibacterial properties depended on their release profile of Zn2+aq ions (Mechanism 2) initially controlled by the different physico-chemical parameters. Moreover, the direct contact mechanism (Mechanism 1) was validated for Zn(II)-based LDHs by comparing the antibacterial activity of micron-sized LDHs against S. aureus to that of LDH nanoparticles (NPs) exhibiting a greater antibacterial effect. The presence of specific surface interactions between Zn(II)-based LDHs and the cell wall of S. aureus was further validated by atomic force microscopy-based force spectroscopy (AFM-FS). The enhancement of the antibacterial properties of Zn(II)-based LDH NPs by ROS generation (Mechanism 3) in presence of UVA light was also assessed. After providing experimental evidences about the three suggested mechanisms, the role of each mechanism contributing to the antibacterial activity of Zn(II)-based LDHs in different antibacterial tests assays was determined

24

Korshed, Peri. "The molecular mechanisms of the antimicrobial properties of laser processed nano-particles". Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/the-molecular-mechanisms-of-the-antimicrobial-properties-of-laser-processed-nanoparticles(731afee1-17f3-4698-b182-b604fb48492f).html.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Microbial resistance to the current available antibiotics is considered a global health problem, especially for the Multi-Drug Resistant pathogens (MDR) including methicillin resistant Staphylococcus aureus. Recently nanoparticles (NPs) have been involved in variety of antimicrobial applications due to their unique properties of antibacterial effects. However, the molecular mechanisms behind their antibacterial activity are still not fully understood. In this study, we produced silver Ag NPs (average size 27 nm) and silver-Titanium Ag-TiO2 NPs (average size 47 nm) using picosecond laser ablation. Our results showed that both laser NPs had obvious size-dependent antibacterial activity. The laser Ag NPs with a size of 19 nm and Ag-TiO2 NPs with a size 20 nm presented the highest bactericidal effect. The laser generated Ag and Ag-TiO2 NPs with concentrations 20, 30, 40, and 50 Î1⁄4g/ml showed strong antibacterial effect against three bacterial strains: E. coli, P. aeruginosa, and S. aureus, and induced the generation of reactive oxygen species (ROS), lead to cell membrane interruption, lipid peroxidation, DNA damages, glutathione depletion and the eventual cell death. Both types of laser NPs at two concentrations (2.5 and 20 Î1⁄4g/ml) showed low cytotoxicity to the in vitro cultured five types of human cells originated from the lung (A549), kidney (HEK293), Liver (HepG2), skin (HDFc) and blood vessel cells (hCAECs). The antibacterial activity of the laser generated Ag and Ag-TiO2 NPs had lasted for over one year depending on the degree of air exposure and storage conditions. Frequent air exposure increased particle oxidation and reduced the antibacterial durability of the laser generated Ag NPs. The laser generated Ag NPs had lower antibacterial activity when stored in cold compared to that stored at room temperature. The antibacterial activity of laser generated Ag and Ag-TiO2 NPs were also compared with four types of commercial based-silver wound dressings (Acticoat TM, AquacelÂ® Ag, Contreet Â®Foam, and UrgotulÂ® SSD) against E. coli to inform future application in this area. In conclusion, laser generated Ag and Ag-TiO2 NPs have strong bactericidal effect and low toxicity to human cells which could be a type of promising antibacterial agents for future hygiene and medical applications.

25

Fàbrega, Santamaria Anna. "Mechanisms of fluoroquinolone resistance in Escherichia coli, Salmonella Typhimurium and Yersinia enterocolitica. Influence on expression of virulence factors". Doctoral thesis, Universitat de Barcelona, 2010. http://hdl.handle.net/10803/283338.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

INTRODUCTION Quinolones are potent and broad spectrum antibacterial agents and, among them, several fluoroquinolones, such as ciprofloxacin, are the treatment of choice against several human infections. Resistance to quinolones is steadily increasing and can be explained by different mechanisms: i) mutations in the target genes, ii) mutations leading to decreased intracellular accumulation of the antibiotic (either by overexpression of efflux pumps or diminished production of porins, the entrance channels for quinolones), and iii) aquisition of plasmid-encoded genes. Acquisition of quinolone resistance is a stepwise process. The first mutation usually leads to nalidixic acid resistance whereas further mutations trigger resistance to fluoroquinolones such as ciprofloxacin. WORK JUSTIFICATION Nalidixic acid resistance is an increasing trend among Escherichia coli, Salmonella Typhimurium and Yersinia enterocolitica clinical isolates thereby compromising the success of antimicrobial therapies. However, ciprofloxacin resistance is not increasing to the same extent in S. Typhimuium and Y. Enterocolitica strains. These results suggest that ciprofloxacin resistance acquisition can somehow impair the bacterial ability in causing disease. Moreover, an in depth study of the mechanisms of fluoroquinolone resistance may lead to the development of new strategies for either combating or reducing the emergence or potential emergence of fluoroquinolone resistance or limiting this effect. OBJECTIVES The main objective of this thesis was to study the molecular mechanisms leading to fluoroquinolone resistance in several pathogens of clinical importance: uropathogenic E. coli and enteric S. Typhimurium and Y. enterocolitica isoaltes. Futhermore, in parallel, the effect of fluoroquinolone resistance acquisition on the expression of several virulence factors (e.g., those leading to invasion and biofilm production) in the two enteric pathogens was evaluated. RESULTS The results obtained in this thesis have led to the publication of four original articles, two manuscripts pending of acceptance in scientific journals and two blocks of additional results. • E. coli: The mechanisms of resistance to fluoroquinolones were studied in two strains: PS5, a susceptible clinical isolate, and NorE5, a fluoroquinolone resistant mutant obtained in vitro (norfloxacin MIC of 32 microg/mL). NorE5 was shown to overexpress the efflux pump AcrAB-TolC attributable to increased SoxS expression likely associated to a mutation within SoxR. Additionally, the mdtG and ompN genes were reported to belong to the soxS regulon. Particularly, the ompN gene is cotranscribed with the upstream gene ydbK. • S. Typhimurium: The prevalence of quinolone resistance mechanisms was evaluated in a collection of Salmonella spp clinical isolates. Almost half of the strains (41.5%) were resistant to nalidixic acid due to a mutation in the target gene gyrA and efflux pump overexpression. Moreover, two S. Typhimurium clinical isolates susceptible to nalidixic acid were selected to obtain in vitro ciprofloxacin resistant mutants (50-64, ciprofloxacin MIC of 64 microg/mL, and 59-64, ciprofloxacin MIC of 256 microg/mL). Strain 50-64 acquired three target gene mutations, overexpressed AcrAB-TolC but showed a reduced fitness as well as invasion on cell culture. Strain 59-64 acquired five target gene mutations, overexpressed the regulator ramA leading to increased efflux independently of AcrAB, which was inactivated in both the clinical and the resistant strain. • Y. enterocolitica: A nalidixic acid-susceptible Y. enterocolitica clinical isolate was selected to obtain in vitro a ciprofloxacin resistant mutant (Y.83-64, ciprofloxacin MIC of 64 microg/mL). The resistant strain acquired four target gene mutations, overexpressed AcrAB-TolC attributable to a mutation in the promoter of the marA homolog (marAYe) present in Yersinia. Moreover, strain Y.83-64 showed reduced invasion. In parallel, the heterogeneity in the selection of target gene mutations was assessed in an intermediate mutant (ciprofloxacin MIC of 4 microg/mL).
INTRODUCCIÓ Les quinolones són antibiòtics d’ampli espectre i gran potència d’entre els quals, algunes fluoroquinolones com la ciprofloxacina, representen el tractament d’elecció per moltes infeccions. La resistència a aquests compostos és deguda a: i) mutacions en els gens diana, ii) mutacions que redueixen l’acumulació interna de l’antibiòtic (sobreexpressió de bombes d’expulsió i descens en la producció de porines), iii) adquisició de gens plasmídics. L’adquisició de resistència a les quinolones és un procés gradual. La primera mutació generalment confereix resistència a l’àcid nalidíxic, mentre que noves mutacions deriven en resistència a la ciprofloxacina. JUSTIFICACIÓ I OBJECTIUS L’increment de resistència a l’àcid nalidíxic en soques d’Escherichia coli, Salmonella Typhimurium i Yersinia enterocolitica és cada vegada més important, tot i que la resistència a la ciprofloxacina en els dos últims patògens no augmenta de manera significativa. Els resultats suggereixen que l’adquisició de resistència podria comprometre la virulència del bacteri. A més a més, un millor coneixement dels mecanismes de resistència pot afavorir l’emergència de noves estràtegies terapèutiques. L’objectiu principal d’aquesta memòria ha estat estudiar els mecanismes moleculars de resistència a les fluoroquinolones en aquests patògens així com el seu efecte en la virulència. RESULTATS • E. coli: Es van estudiar els mecanismes de resistència a les fluoroquinolones en dues soques: PS5, un aïllat clínic sensible, i NorE5, un mutant resistent a la norfloxacina. Es va identificar la sobreexpressió de la bomba AcrAB-TolC en NorE5 atribuïble a la sobreproducció de SoxS, originada per una mutació en el regulador SoxR. A més a més es van caracteritzar dos gens nous que pertanyen al reguló de SoxS: mdtG, que codifica per un sistema transportador, i ompN, que codifica per una porina i es coexpressa amb ydbK. • S. Typhimurium: Es va avaluar la prevalença dels mecanismes de resistència a l’àcid nalidíxic en un grup de soques clíniques de Salmonella spp. El 41.5% de les soques eren resistents amb una mutació en el gen gyrA i la sobreexpressió de bombes d’expulsió. Alternativament, es van seleccionar dues soques clíniques de S. Typhimurium (50-wt i 59-wt) sensibles a l’àcid nalidíxic per obtenir en el laboratori els corresponents mutants resistents a la ciprofloxacina (50-64 and 59-64). La soca 50-64 va adquirir 3 mutacions en el gens diana, sobreexpressava AcrAB-TolC, tenia una capacitat invasiva molt reduïda així com un creixement inferior a l’habitual. La soca 59-64 va adquirir 5 mutacions en els gens diana, sobreexpressava el regulador ramA associat a la sobreexpressió d’una bomba desconeguda, doncs tenia AcrAB inactivat per una mutació interna ja en la soca clínica original. • Y. enterocolitica: Es va seleccionar un aïllat clínic sensible a l’àcid nalidíxic per obtenir un mutant resistent a la ciprofloxacina (Y.83-64). La soca resistent va adquirir 4 mutacions en els gens diana, sobreexpressava AcrAB-TolC, atribuïble a la sobreexpressió de marAYe degut a una mutació en el promotor, i va mostrar un descens en la capacitat invasiva. Alternativament, es va avaluar l’heterogeneïtat en la selecció de mutacions en els gens diana en un mutant amb menor resistència a la ciprofloxacina.

26

Yu-ChiehChou e 周鈺捷. "Mechanism of Antibacterial Activity of Photochemically Transformed Graphene Oxide". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/8bu7v2.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

碩士
國立成功大學
環境工程學系
104
This work examined the mechanism behind the antibacterial activity of graphene oxide (GO) before and after phototransformation in sunlight conditions. Our previous research has shown that GO can be phototransformed under simulated sunlight exposure, forming products with progressively reduced sizes and oxygen-containing functionalities. Depending on the phototransformation conditions, GO could become more toxic, while the toxicity was negated after phototransformation in the presence of H2O2 (i.e., indirect photolysis). While the finding is interesting and could aid in assessing the ecological impact of GO, the mechanism is not completely clear. This is the motivation of this study. New techniques including the antibacterial test of GO materials deposited on surfaces, cell morphology, membrane integrity using fluorescence dyes, and antioxidant effect, and reactive oxygen species (ROS) detection were developed and used to shed mechanistic light on the altered toxicity after phototransformation. The results indicate that bacteria incubated with phototransformed GO deposited on surfaces showed increased growth inhibition. The enhanced toxicity could be attributed to the reduced functional groups and/or sizes of GO after phototransformation. Greater cell deformation and increased membrane permeability correlated with larger extent of GO phototransformation. The growth of bacteria incubated with GO materials and antioxidants including natural organic matter (NOM) increased, indicating that oxidative stress likely plays a role. Collectively, the results indicate that phototransformation enhanced antibacterial activity is associated with oxidative stress that increases with the degree of phototransformation.

27

Singh, Jagriti. "Antibacterial Surfaces Mechanisms, Design and Development". Thesis, 2021. https://etd.iisc.ac.in/handle/2005/5470.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

The spread of disease-causing microorganisms through high-touch surfaces and their increased tolerance against antimicrobials and the host immune system is responsible for several fatal diseases. By the year 2050, Antimicrobial resistance (AMR) is expected to cause 10 million deaths annually and a loss of US$100 trillion. Today, some bacterial species (e.g., Carbapenem-resistant Enterobacteriaceae group of bacteria) are immune to all major classes of available antibiotics. This has encouraged the scientific community to develop alternatives to antibiotics to fight the AMR. Primary sources of spread and resistance acquisition among bacteria include cross-contamination of surfaces in hospitals, catheters, stethoscopes, and surgical tools. Any such abiotic surface is vulnerable to bacterial colonization that begins with a few primary colonizers attaching themselves to the surface to condition it for further attachment of arriving bacteria. After initial attachment, bacteria start to proliferate and develop into surface-bound colonies. It then forms a robust protective layer of biofilm that brings advantages to bacterial survival against environmental odds. Hence, the initial stage of attachment is a weak link in the bacterial journey to forming a protective biofilm. Exploiting this weak link, nanostructured surfaces hinder initial attachment by physically rupturing the cell without the involvement of any chemical or biocides, hence are consistently called “promising” in controlling bacterial proliferation. Although various theories over the past few years have tried to explain the behavior of bacteria on these nanostructures, there is a lack of consensus on the precise mechanism that leads to bacterial death. To efficiently restrain bacterial colonization, it is of profound importance to understand the fundamental cause of bacterial death on these nanopillars. Only such fundamental understanding can guide us to the answer to the question: What precise nanopillars feature participate in bacterial cell-rupture and how? In this doctoral dissertation, we investigated the mechano-response of E. Coli cells as it attaches itself to a regular array of precise dimension-controlled nanopillars. Overcoming the fabrication limitations, two sets of ordered arrays of nanopillars by varying one dimension at a time makes it possible to study the involvement of individual dimensions on the response of single bacterial cell, which is crucial in understanding the rupture mechanism. The bacterial cell extends out via thread-like projections in the direction of neighboring pillars to establish contact with them. At a particular interpillar spacing (pitch) of straight pillars, the attached nanopillars appear to bend towards the cell due to the application of force. This displacement of pillars and hence the force increases with interpillar spacing. Bactericidal efficacy was proportional to the applied force, and hence interpillar spacing. The method of calculating force applied by bacteria on nanopillars adds direct experimental evidence towards the proposed mechanism of bacterial interaction with nanopillars at the single-cell level. We have focussed on one bacterial strain E. Coli; however, this method of studying bacterial-nanopillar interaction can pinpoint the governing parameter for cell rupture for different bacterial strains. After establishing the fundamentals of mechano-bactericidal mechanism, the subsequent work progresses to dual action antibacterial surfaces that aim towards studying alternatives to biocide coatings aiding from mechanical rupture of cells. A common non-selective way to kill bacteria without using antibiotic chemicals, and hence following the risk of developing antibacterial resistance, is to use photocatalytic materials. They produce reactive oxygen species (ROS) in the presence of light and water that cause bacterial death on the surface. The dual action surfaces benefit from nanostructures and photocatalytic antibacterial coatings over it. We establish the design principles of such “dual-action” surfaces, and answer several open questions, for example: which material should the nanostructures be made of? What is the optimum photocatalyst thickness? What geometries are most effective? In this work, TiO2 is used as the photocatalytic coating on nanostructures made of Si and SiO2. It is demonstrated that TiO2-coated “black-silica" (nanostructured SiO2), is more effective in producing the bactericidal effect. The bacterial kill rate is improved by 73% on replacing the underlying Si nanopillars with SiO2 nanopillars. To understand the dynamics of light absorption and subsequent ROS diffusion in such systems, FDTD and FEM simulations were used for modeling. FDTD simulations show that parasitic absorption in the underlying base pillar of high extinction coefficient leads to significant loss of incident optical energy. Hence, the “total absorption” of a system can be a misleading proxy for photocatalytic activity. Only absorption in the photocatalyst (TiO2) matters, which can be enhanced by fabricating nanopillars with a more transparent material like SiO2 or PDMS, having a low extinction coefficient. Further, FDTD coupled with FEM simulations shows that taller nanopillars don’t always lead to higher bulk ROS concentration, despite more absorption. Beyond 5 µm height, ROS are unable to diffuse out of the nanopillar forest. After articulating the design rules, the next step is to come up with a scalable process that can be deployed as practical antibacterial surfaces. In this work, we further extend the effectiveness of the TiO2-coated B-Si. By substituting TiO2 with TiO2 nanoparticles, the effective surface area for the production of ROS increases significantly. The extraction of photocarriers also improves because bulk of TiO2 is always within a few nm of a surface. The films are fabricated with three different techniques, all of which are scalable to large-areas. We establish the impact of the different techniques on the film’s topology and ability to kill bacteria. Antibacterial photocatalytic coatings are a promising alternative; however, the band gaps of most metal oxides are too wide, requiring UV/blue illumination. To deal with this, we discovered a new antibacterial photocatalyst, Mn2V2O7 (MVO), that works in ambient light or low-intensity solar radiation. The β-phase has a bandgap of 1.7 eV, so MVO absorbs visible light up to 600 nm.7 Under visible light, MVO reduces bacterial load by four orders of magnitude. MVO can be coated into films by drop-casting, which kills 76% of bacteria. In conclusion, work done in this thesis address the problem of spread of antimicrobial resistant bacteria via surfaces. We establish the mechanism of interaction of bacteria with nano-pillars also called as mechano-bactericidal mechanism. This formulates the understanding behind contact-kill mechanism of nanostructures. We extended efficiency of nanopillars by coating it with photocatalytic material that non-selectively degrades any organic material including bacterial cells, hence adds as a second line of defense again bacterial colonization. Using FEM and FDTD simulations, we articulated the design rules of such coated nanostructures. We developed technique to coat mesoporous photocatalyst on these nanostructures allowing larrge area deployment. At last, we overcame the UV-activated limitation of photocatalysts by enabling a visible light-activated antibacterial material suitable for large area coatings.
MHRD, DST

28

LI, HAN-LIN, e 李函陵. "Antibacterial Mechanism of Novel Cationic Antimicrobial Peptides against Multidrug-Resistant Escherichia coli". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/2jq4u9.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

碩士
國立宜蘭大學
生物技術與動物科學系動物科學碩士班
102
Escherichia coli is a Gram-negative bacterium commonly found in human and animal intestinal commensal, mainly parasitic in the large intestine. Intestinal pathogenic E. coli causes a wide variety of severe infectious diseases in humans and animals, such as urinary tract infections, meningitis, peritonitis, septicemia, bacterial pneumonia and diarrhea in neonate and weaning piglets. Moreover, its remarkable ability to acquire resistance against most of commercially available antibiotics has led to a global threat to human health. Abuse of classical antibiotics has led to the mass production of multidrug-resistant (MDR) bacterial strains. Antimicrobial peptides (AMPs) have been reported to exert their cytolytic activity by folding into an amphipathic helix upon selectively binding and insertion into the negatively charged bacterial membrane, leading to breakdown of the membrane structure, thus causing leakage of cell contents, resulting finally in cell death. Recent studies indicated that AMPs may serve as a promising solution to combat MDR microbial infections. In our previous studies, we have designed and synthesized a series of novel cationic AMPs with high antibacterial activity and selectivity against a broad spectrum of Gram-positive and Gram-negative bacteria. In the current study, the antibacterial activity of these AMPs against wild-type (WT) and drug-resistant (1R and 8R) E. coli was evaluated. Minimum inhibitory concentration (MIC) measurement revealed that GW-H1-a exhibited the best antibacterial activity, showing lower MIC values against higher resistant strains, 8R (2ug/ml), 1R (4ug/ml) and WT (8ug/ml). In order to decipher the responsive mechanism of WT and MDR E. coli against antibacterial agents, whole protein profile and the sub-proteome (including outer membrane, inner membrane and cytoplasmic proteins) of WT and 8R were extracted and investigated using two dimensional gel electrophoresis (2-DE)-based proteomic approaches. Protein spots with significantly altered expression level as revealed by image analysis were subjected to LC-ESI-Q-TOF MS/MS and identified by Mascot program. Furthermore, lipopolysaccharide (LPS) competition analysis was applied to verify if LPS is the major binding target when AMPs approach and adhere to the bacterial surface. According to the findings in this study, we may evaluate the feasibility of these AMPs as novel agents against MDR strains.

29

Chang, Shun-Hsien, e 張順憲. "Antibacterial and antimutagenic activity and mechanism of chitosan with various molecular weights". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/xw3rd8.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

30

Chang, Wei-Ting, e 張媁婷. "The study of antibacterial activity and mechanism of Para-hydroxybenzoic acid ester". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/94120588850540247687.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

碩士
萬能科技大學
化妝品應用與管理研究所
104
Cosmetics may are contaminated with spoilage microorganisms. The necessary of add preservative in cosmetic, to preserve the pollution caused by bacteria and mould, but preservatives must not be added to products in amounts which may jeopardize the safety of human beings, and that consideration must be given to minimizing the amount of preservatives used. Their activity would be influenced by other cosmetic ingredients such as surfactants. The purpose of this study is evaluating the minimum inhibitory concentration (MIC) of methyl paraben and butyl paraben and the interaction with Tween nonionic surfactants. The methyl paraben and Butyl paraben and Phenoxyethanol and Methylisothiazolinone and Imidazolidinyl urea are widely used in cosmetics as preservatives. The minimum inhibitory concentration of methyl paraben and Butyl paraben and Phenoxyethanol and Methylisothiazolinone and Imidazolidinyl urea against Pseudomonas aeruginosa and Staphylococcus aureus can be to reduce the amount of preservatives used. Furthermore, explore the interaction of nonionic surfactants and preservative, the results found Tween 20 and methyl paraben exhibited synergistic effect that against S. aureus. The above results show, the synergistic effect of Tween 20 and methyl paraben is useful for cosmetic modulation that can diminish preservatives concentration. But mechanism of action of this phenomenon is not clear. The mechanism of parabens as antimicrobial agents the phenomenon is reversible. Our result suggested Tween 20 disrupts cell membrane structure and enhances the bactericide effect of methyl paraben.

31

Chen, Hsiu-Chi, e 陳綉琪. "Antibacterial Mechanism of Novel Cationic Antimicrobial peptides against Multidrug-Resistant Acinetobacter baumannii". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/74668514967054529548.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

碩士
國立宜蘭大學
生物技術與動物科學系生物技術碩士班
101
Acinetobacter baumannii (A.b) is a non-fermentative Gram-negative bacterium, which causes awide variety of severe nosocomial infections including pneumonia, bacteremia, urinary tract infection and wound infection in immunocompromised patients with increasing frequency andhigh mortality rate. Moreover, its remarkable ability to acquire resistance against most of commercially available antibiotics has led to a global threat to human health. Recent studies indicated that antimicrobial peptides (AMPs) may serve as a promising solution to combat multidrug-resistance microbial infections. In our previous studies, we have designed and synthesized a series of novel cationic AMPs with high antibacterial activity and selectivity against a broad spectrum of Gram-positive and Gram-negative bacteria. In the current study, we seek to evaluate their potency against wild-type (wt) and several multidrug-resistant (MDR) A.b strains. Proteomic approaches were applied to reveal the differences in protein profiles between wt and MDR strains. MIC analysis was performed to evaluate the antibacterial efficacy of these AMPs against wt and MDR strains. The results showed that our AMPs were potent against MDR strains (MIC values of 2 μg/mL), as compared to that of the wt (4 μg/mL). Two-dimensional gel electrophoresis was performed as triplicates in three independent experiments. Image analysis revealed several protein spots significantly altered among wt and MDR strains. These protein spots have been in-gel digested by trypsin and then subjected to LC-ESI-Q-TOF MS/MS analysis. Proteins identified could help delineating the interaction between AMPs and pathogens. Cell infection studies are now under investigation. Lipopolysaccharide (LPS) competitive assay revealed that LPS may be the reaction target of AMPs on the bacterial surface. In the current study, a series of novel cationic AMPs were confirmed to possess potent antibacterial activity against A.b MDR strains. These findings would provide support for future application of these novel AMPs as potential therapeutic agents for treatment of infections by MDR bacterial strains.

32

CHANG, YA-YUN, e 鄭雅勻. "Using Shotgun Proteomics to Elucidate the Antibacterial Mechanism by Protein Carbonylated Modification". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/67sech.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

33

"In Vitro and In Vivo Assessment of the Mechanism of Action and Efficacy of Antibacterial Clays for the Treatment of Cutaneous Infections". Doctoral diss., 2014. http://hdl.handle.net/2286/R.I.24926.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

abstract: The prevalence of antibiotic resistant bacterial pathogens has increased since the introduction of penicillin in the 1940s. Insufficient development of novel antibacterial agents is leaving us with a failing arsenal of therapies to combat these pathogenic organisms. We have identified a clay mineral mixture (designated CB) that exhibits in vitro antibacterial activity against a broad spectrum of bacterial pathogens, yet the antibacterial mechanism of action remains unknown. Antibacterial susceptibility testing of four different clay samples collected from the same source revealed that these natural clays had markedly different antibacterial activity. X-ray diffraction analyses of these minerals revealed minor mineralogical differences across the samples; however, ICP analyses demonstrated that the concentrations of many elements, Fe, Co, Cu, Ni, and Zn in particular, vary greatly across the four clay mixture leachates. Supplementation of a non-antibacterial leachate containing lower concentrations of Fe, Co, Ni, Cu, and Zn to final ion concentrations and a pH equivalent to that of the antibacterial leachate resulted in antibacterial activity against E. coli and MRSA, confirming the role of these ions in the in vitro antibacterial clay mixture leachates. The prevailing hypothesis is that metal ions participate in redox cycling and produce ROS, leading to oxidative damage to macromolecules and resulting in cellular death. However, E. coli cells showed no increase in DNA or protein oxidative lesions and a slight increase in lipid peroxidation following exposure to CB-L. Supplementation of CB-L with ROS scavengers eliminated oxidative damage in E. coli, but did not rescue the cells from killing, indicating that in vitro killing is due to direct metal toxicity and not to indirect oxidative damage. Finally, we ion-exchanged non-antibacterial clays with Fe, Co, Cu, and Zn and established antibacterial activity in these samples. Treatment of MRSA skin infections with both natural and ion-exchanged clays significantly decreased the bacterial load after 7 days of treatment. We conclude that 1) in vitro clay-mediated killing is due to toxicity associated directly with released metal ions and not to indirect oxidative damage and 2) that in vivo killing is due to the physical properties of the clays rather than metal ion toxicity.
Dissertation/Thesis
Ph.D. Microbiology 2014

34

En-ChiWu e 吳恩綺. "The antibacterial mechanism of photodynamic therapy on bacterial pathogen: oxacillin-resistant Staphylococcus aureus as a model organism". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/9wnnrs.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

碩士
國立成功大學
生物化學暨分子生物學研究所
101
Antibiotic-resistant bacterial infection has become a severe global problem. Oxacillin-resistant Staphylococcus aureus (ORSA) is one of the major bacterial pathogens causing hospital-acquired bacterial infections. In this study, ORSA was used as a model to study the molecular mechanisms and possibilities of overcoming drug resistance by photodynamic therapy (PDT). PDT with indocyanine green (ICG), a photosensitizer, was used to inhibit the growth of ORSA in vitro. The safety of the regimen was examined on human fibroblasts. Bacterial virulence including the activities of coagulase, enterotoxin and protease was investigated after PDT. The sensitivity to oxacillin was examined by disk diffusion method. Reactive oxygen species (ROS) enhancers (D2O and H2O2) and scavengers (tryptophan and ascorbic acid) were added during PDT to evaluate whether oxidative stress was involved in PDT. The morphology of bacteria after ICG-PDT was observed by transmission electron microscopy (TEM). A 2 log10 growth inhibition of ORSA was observed after 200 J/cm2 infrared irradiation at 65.5 mW/cm2 in the presence of 25 g/ml ICG. This condition showed no phototoxicity in human fibroblasts. PDT significantly reduced bacterial virulence including coagulase and enterotoxin, but not protease. This change might be related to the reduction of viable bacteria after PDT. Interestingly, PDT increased the susceptibility of ORSA to oxacillin. The drug sensitive phenotype persisted for at least 14 passages. The inhibition of cell growth was mediated partly through the ROS generated during PDT. TEM showed severe cell destruction immediately after irradiation. In conclusion, PDT may have potential to become a new alternative or adjuvant therapy against ORSA. Whether gene mutation is involved in the molecular mechanism merits further exploration.

35

LIN, LI-YANG, e 林立揚. "Studies on antimicrobial activity and mechanism of nisin in combination with cationic antibacterial agents against Staphylococcus aureus". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/yxw3qk.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

碩士
國立宜蘭大學
食品科學系碩士班
105
Staphylococcus aureus, a facultative Gram-positive coccus, is one of the most common causes of foodborne illness. Due to the fact that the abuse of antibiotics has facilitated the occurrence of the antibiotics resistant strains, the combining use of antibacterial agents with different mechanisms has been recognized as the most promising strategy in reducing the risk of antibiotics resistance. Nisin (Ni), a 34-residue-long antibacterial peptide, was approved by the US FDA for use in food products. It is bactericidal against many Gram-positive bacteria by the inhibition of peptidoglycan biosynthesis and membrane pore formation. In this study nisin was utilized as the base to conduct combination tests with cationic antibacterial agents of different antibacterial mechanisms, including pepsin-hydrolyzed Lactoferrin hydrolysates (LfH), lactoferricin (Lfcin), ε-Polylysine (PL), and Daptomycin (Da), against two S. aureus strains and one Methicillin-resistant S. aureus (MRSA) strain. The antibacterial activity were determined by the minimum inhibitory concentration (MIC) test, determined by using a 96-well microplate; the interactions between two antibacterial agents against strains were determined by a checkerboard microtitration method and fractional inhibitory concentration (FIC) index; kinetic antibacterial growth curve test, and the results revealed nisin combining LfH has a great synergistic effect against all three tested strains; whereas, combination result for Ni/PL, Ni/Da, LfH/PL, LfH/Da, Ni/Lfcin and PL/Da showed partial or no synergistic effect. Besides, according to MIC test, the uptake of L-alanine could enhance the sensitivity of S. aureus to nisin due to the reduction in the negative charge on the bacterial surface and it could reduce 34%, 22% of nisin used against the S. aureus 780, 451 strains.; however, there was no significant effect on FIC index in combination tests. By analyzing the potassium ions (K+) release from bacteria treated with antibacterial substances, it showed that nisin and ε-polylysine could obviously cause K+ released from tested strains, however daptomycin and LfH was comparatively insignificant. The combination of nisin and LfH could lead S. aureus and MRSA strains more K+ loss than in single treatment. According to the morphological change of the tested strains observed in scanning electron microscope (SEM), antibacterial agents showed different antibacterial behaviors; besides, the combination of nisin and LfH demonstrated a complete lysis of target cells, than single used. To sum up, nisin may play a role as a major attacker and LfH as an enhancer in synergistic antibacterial activity against S. aureus and MRSA.

36

Schlee, Miriam [Verfasser]. "Probiotic bacteria enhance the antibacterial barrier of enterocytes : insights into their mechanism of action / vorgelegt von Miriam Schlee". 2007. http://d-nb.info/984510567/34.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

37

CHANG, TIEN-YAO, e 張天耀. "Investigating the regulatory mechanism of efflux pump and antibacterial activity of silver nanoparticles for multiple drug resistant Acinetobacter baumannii". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/8a4qwn.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

博士
國防醫學院
醫學科學研究所
105
Part 1 Acinetobacter baumannii is an increasing threat of nosocomial infections in recent years, especially the emergence of multi-drug resistant strains (multi-drug resistant Acinetobacter baumannii; MDRAB). Infections caused by multi-drug resistant A. baumannii could cause longer hospital stay and higher treatment costs. Tigecycline, a board-spectrum tetracycline derivative, is considered as the last antibiotic choice for the MDRAB. However, resistance to Tigecycline was reported following the drug usage worldwide. These resistances are mainly associated with overexpression of efflux pump, especially AdeABC, which is regulated by a corresponding two-component system AdeRS. In the research, we found that the regulatory factor AdeR could recognize the direct repeat on intercistronic region between adeR and adeA. This interaction inhibits the downstream efflux pump expression. In addition, mutations on AdeR DNA binding domain show lower affinity to the direct repeat sequences, and elevate the expression level of efflux pump, leading to high resistance to tigecycline (MIC = 16 μg/mL). This result is very useful for understanding the mechanism of tigecycline resistance of A. baumannii. Part 2 We generate a silver nanoparticles using green synthesis. In this process, silver nitrate is used as a precursor of silver ions, and then glucose and trimethyl nitrate chitosan (TMCN) are used as a reducing agent and stabilizer, respectively. The whole reaction of silver nanoparticle synthesis could be done at room temperature after adding alkaline solution and mixing thoroughly. There is no need to consume energy or to use expensive equipment. Adjusting the concentration of sodium hydroxide, glucose and TMCN will affect the particle size, zeta potential and formation yield of silver nanoparticles. The average size of this silver nanoparticles (TMCN-AgNPs) is around 60 nm with positive surface charge. The physical and chemical properties of this nanoparticles were characterized by UV-Vis spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The catalytic activity of TMCN-AgNPs was determined by reduction of 4-nitrophenol using NaBH4 as a reducing agent. The antibacterial activity of TMCN-AgNPs was evaluated by broth microdilution method, and was proved to have antibacterial activity against Acinetobacter baumannii, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. The minimum inhibitory concentration (MIC) was < 6.13 μg/mL. Moreover, TMCN-AgNPs also showed antibacterial activity against multidrug-resistant Acinetobacter baumannii from clinical isolated, and the MIC value was < 12.25 μg/mL.

38

Tseng, Pin Wen, e 曾品文. "Investigation of the Role of PBP1a, PBP1b and PBP3 on Antibacterial Mechanism of Sulbactam Against Acinetobacter baumannii ATCC 19606". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/37996767316260981250.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

碩士
國立清華大學
分子醫學研究所
104
Over the past several decades, the overuse of antibiotics leads to the development of multidrug resistance in pathogens. Many bacteria can resist beta-lactam antibiotics by disrupting the beta-lactam ring of the drugs with -lactamase. To counter the effects of -lactamase, scientists have developed -lactamase inhibitors which protect beta-lactam antibiotic from degradation by irreversible binding with -lactamase. Beta-lactamase inhibitors do not exhibit strong antibacterial activity if given alone. Interestingly, it was noted recently that sulbactam, a -lactamase inhibitor, can inhibit growth of Acinetobacterium baumannii, a human opportunistic pathogen, although the mechanism remains not clear. To explore the antibacterial mechanism of sulbactam, this study first isolated sulbactam resistant strains (SRSs) of A. baumannii ATCC 19606, and then determined their minimal inhibitory concentration of sulbactam. These sulbactam-resistant strains grew slower and appeared longer. Comparison of sulbactam affinity to penicillin-binding proteins between ATCC 19606 and SRSs showed no difference. Introduction of pbp1a, pbp1b and pbp3 gene of Pseudomonas aeruginosa PAO1, a sulbactam resistant bacterium, into A. baumannii ATCC 19606 individually did not confer the recipient sulbactam resistance. Sequence analysis of pbp1a, pbp1b and pbp3 gene of A. baumannii ATCC 19606 and its SRSs also revealed no difference. It conclusion, this study is unable to identify a direct role of PBP1a, PBP1b and PBP3 in growth inhibition of A. baumannii by sulbactam.

39

LANG, CHEN RUEI, e 陳瑞瑯. "A study on mechanism of Antibacterial Activity and properties of degree of deacetylation of Chitosan laminated on Thermoplastion Polyurethane Films". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/96624289351759763046.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

碩士
國立臺灣科技大學
高分子工程系
91
The objects of this study is to investigate the influence of the degree of deactylate (D.D.)of chitosan on antibacterial activity and performance of chitosan /TPU(Thermoplastic polyurethane) composites. The experiment is carried out by antibacterial examination, DMA (Dynamic Mechanical Analysis) and TGA (Thermo Gravimetric Analyzers) and mechanical performance tests for crosslinking chitosan films, chitosan/TPU lamination films and chitosan/TPU blends. From the series experiments, we find the D.D. of chitosan the antibacterial activity mechanical performance increased with the D.D. of chitosan increased. On the other hard, the good interfacial behavior ﹠mechanical properties also observed in chitosan and TPU lamination films.

40

Hayes, Andrew James. "Biotin protein ligase inhibitors as new antibacterial agents to target Staphylococcus aureus: Studies of efficacy, mechanism of action and resistance". Thesis, 2017. http://hdl.handle.net/2440/121937.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

There is a desperate need for new antibacterials to combat the growing threat of antimicrobial resistant infections. One of the most common causes of such infections is the Gram-positive pathogen Staphylococcus aureus. S. aureus is responsible for the majority of hospital based infective deaths, with strains resistant to even last resort antibacterial agents. To combat these infections novel antibiotic agents are required. However, few novel antibacterial agents have been approved in the past 4 decades, with most products being derivatives of previously used chemical classes. As a result, resistance mechanisms are often already present in bacteria, or develop rapidly after introduction. Antibacterial agents with novel mechanism of action against S. aureus are needed to address this crisis. One potential target for the development of novel antibacterials is the essential enzyme biotin protein ligase (BPL). The BPL of S. aureus serves two major functions. Firstly, BPL catalyses attachment of the vitamin biotin onto biotin-dependent enzymes, such as acetyl-CoA (ACC) and pyruvate carboxylase (PC). Secondly BPL is a transcriptional repressor that regulates expression of proteins required for biotin biosynthesis and biotin transport. Previous work in our laboratory and others has sought to generate inhibitors that target BPL catalytic activity, however little is known about their effect on transcriptional repression. As a result, several BPL inhibitors with a variety of chemical scaffolds are described in the literature focusing on creating mimics of the reaction intermediate biotinyl-5′-AMP. Despite success in creating antibacterial inhibitors, a selective compound that completely inhibits bacterial growth has proved elusive. The most potent and selective anti-staphyloccocal compound, biotin-triazole, shows promising inhibitory activity (Ki = 90 nM) but is unable to completely inhibit bacterial growth. The first aim of this thesis is to characterise three distinct chemical classes of BPL inhibitors designed to improve whole cell antibacterial activity. Each series of inhibitors was tested to determine in vitro potency and whole cell efficacy through enzyme and antibacterial susceptibility assays. The first and second compound series are modifications of the previously described biotin-triazole pharmacophore. Series 1 describes the shortening of the triazole pharmacophore with a view to producing a refined pharmacophore with greater drug like properties. For a similar purpose series 2 was created by halogenation of the C5 position on the triazole ring. Improvements in whole cell activity were achieved in series 2, yielding our first biotin-triazole inhibitor to completely inhibit bacterial growth (MIC = 8μg/ml). The third series tested a separate sulfonyl based compound series and provided the most potent BPL inhibitor and antibacterial to date. This compound, BPL 199, exhibited a sub-nanomolar Ki (0.7 nM) and an MIC of < 0.5 μg/ml against a panel of S. aureus isolates. Importantly, BPL199 also showed no cytotoxicity against two human cell lines, HepG2 and HEK293, and was well tolerated in mouse models. The second aim of this thesis was to validate the mechanism of antibacterial action of BPL inhibitors and investigate potential mechanisms of resistance in S. aureus. To validate the mechanism of action, a BPL overexpression strain was constructed in S. aureus strain RN4220 and used to test the effect of increased BPL on compound efficacy. This system was used against the most potent compounds from all three series. The assay confirmed that BPL inhibitors exerted antibacterial effects through inhibition of the BPL enzyme for the most potent antibacterial compounds. To determine resistance mechanisms to BPL inhibitors in S. aureus several individual isolates of S. aureus NCTC 8325 were exposed to sub-optimal concentrations of BPL199 to evolve resistance. Whole genome sequencing of the strains resistant to BPL199 was then undertaken to identify potential resistance mechanisms. The mutations present occurred in a diverse range of genes including BPL and the biotin dependent enzyme pyruvate carboxylase. The one missense mutation in BPL (D200E) was further explored with both in vitro and in vivo testing. This amino acid substitution was found to not greatly affect catalytic activity, reducing the affinity for biotin by 2-fold (Km wt = 1.8 ± 0.3 μM , D200E = 3.8 ± 0.4 μM) and did not affect repression by the inhibitor (Ki wt = 4.8 ± 2.1 nM , D200E =10.9 ± 3.5 nM). However native mass spectrometry was able to show that the substitution abolished dimerization of the BPL in vitro and EMSA showed that this resulted in reduced DNA binding activity. Further in vivo testing, with a chromosomally integrated lacZ reporter assay in E. coli, demonstrated that the mutation was sufficient for dysregulation of the biotin transport and synthesis genes with a greater than 50 – fold increased biotin concentration required to facilitate repression of biotin transport. Several of the other mutations identified, such as the one in PC, were likely to induce loss of function. The individual effect of a loss of function in these genes was further explored using transposon mutagenesis knock-out strains. The effect of individual loss of function mutations in pyruvate carboxylase in S. aureus JE2 determined that this mutation alone was sufficient for a four-fold decrease in susceptibility to BPL199. In summary this thesis has looked at the development of BPL inhibitors for the purpose of antibacterial drug discovery. Using the most potent compounds the mechanism of action and resistance to BPL inhibitors was also characterised. This work will help in the future design of BPL inhibitors with the resistance mechanisms suggesting potential pathways that are important for BPL inhibitor resistance.
Thesis (MPhil) -- University of Adelaide, School of Biological Sciences, 2017

41

Nautiyal, Astha. "Understanding the Mechanism of Homologous Recombination in Mycobacterium Tuberculosis : Exploring RecA as an Antibacterial Target and Characterization of Holliday Junction Resolvases". Thesis, 2015. http://etd.iisc.ac.in/handle/2005/3986.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Homologous recombination (HR) is conserved across all three domains of life and is associated with a number of key biological processes. Over the years, numerous genetic, biochemical and structural studies have uncovered important mechanistic details and established a role for HR in DNA damage repair, control of DNA replication fidelity and suppression of various types of cancer. Much of our current understanding of the mechanistic aspects of HR is gained from the study of Escherichia coli paradigm. E. coli RecA is the founding member of a nearly ubiquitous family of multifunctional proteins and is substantially conserved among eubacterial species. During HR, RecA protein promotes homologous pairing followed by strand exchange reaction leading to heteroduplex formation. In addition to HR, RecA is a central component of SOS response, recombinational DNA repair and rescue of collapsed replications forks. Moreover, recent work has suggested that DNA recombination/repair mechanisms might contribute to genome evolution and consequently to the generation of multidrug-resistant strains of the pathogen. The disease caused by Mycobacterium tuberculosis, endemic in certain regions of the world, is a leading cause of disability and death. A thorough knowledge of the function and interaction of specific HR proteins/enzymes involved in the maintenance of genome integrity is essential in order to elucidate the impact of genome perturbation effects on M. tuberculosis. Toward this end, modulation of RecA protein activity, a central component of HR, represents a potential novel target for design of new drugs because of its involvement in various processes of DNA metabolism. Additionally, small molecule modulators of RecA activity may offer novel insights into the regulation and its role in cellular physiology and pathology. Traditionally, antibiotics have been used to treat infections caused by bacteria. Despite their importance, the development of new antibiotics against M. tuberculosis has considerably decreased over the past several years due to disappointing results in clinical trials. These failures may be due the fact that they suffer from low potency or low cell permeability. Therefore, one of the aims of studies described in this thesis was to test the effect of suramin, a known inhibitor of E. coli RecA, on various biochemical activities of mycobacterial RecA proteins and determine its mechanism of action. Furthermore, the most crucial step in the HR pathway and rescue of collapsed DNA replication forks is the resolution of Holliday junctions and other branched intermediates. Because Holliday junction resolvases are essential for the resolution of different types of DNA recombination/repair intermediates, therefore, we considered it worthwhile to study the genomic expression and biochemical properties of HJRs in M. tuberculosis. Suramin is a commonly used antitrypanosomal and antifiliarial drug, and a novel experimental agent for the treatment of several cancers. A forward chemical screen assay identified several small molecule inhibitors of E. coli RecA. In this screen, suramin (also called germanin), a polysulfonated naphthylurea, and suramin-like agents were found to inhibit EcRecA catalyzed ATPase and DNA strand exchange activity. However, the mechanism underlying such inhibitory action of suramin and whether it can exert antibacterial activity under in vivo conditions remains largely unknown. In an attempt to delineate the range of suramin action, we reasoned that it might be useful to test its effect on mycobacterium RecA proteins. We found that suramin is a potent inhibitor of all known biochemical activities of mycobacterial RecA proteins with IC50 values in the low μM range. The mechanism of action involves, in part, its ability to disassemble the nucleoprotein filaments of RecA-ssDNA. To validate the above results and to obtain quantitative data, a pull-down assay was developed to assess the effect of suramin on RecA–ssDNA filaments. The data indicated that suramin was able to dissociate >80% of RecA bound to ssDNA. Altogether, these results indicated the effectiveness of suramin in the disassembly of RecA nucleoprotein filament. Next, we sought to test whether suramin binds to RecA by using a CD spectropolarimeter. Significant spectral changes were observed upon addition of increasing concentrations of suramin, indicating alterations in the secondary structure of RecA protein. Additional evidence revealed that suramin impaired RecA catalyzed proteolytic cleavage of LexA repressor and blocked ciprofloxacin-inducible recA gene expression and SOS response. More importantly, suramin potentiated the cidal action of ciprofloxacin and reduced the growth of Mycobacterium smegmatis recA+ strain but not its isogenic recA∆ mutant, consistent with the idea that it acts directly on RecA protein. This approach, which appears as an appealing concept, opens up new possibilities to chemically disrupt the pathways controlled by RecA and treat drug-sensitive as well as drug-resistant strains of M. tuberculosis for better infection control and the development of new therapies. The annotated genome sequence of M. tuberculosis revealed the presence of putative homologues of E. coli DNA recombination/repair genes. However, it is unknown whether these putative genes have the ability to encode catalytically active proteins or participate in biochemical reactions intrinsic to the process of HR or DNA repair. Studies in the second half of the thesis originated from an in silico analysis for genes that encode functional equivalents of E. coli RuvC HJ resolvase(s) in M. tuberculosis. The central intermediate formed during mitotic and meiotic recombination is a four-way DNA junction, also known as the Holliday junction (HJ), and its efficient resolution is essential for proper segregation of chromosomes. The resolution of HJ is mediated by a group of structure specific endonucleases known as the Holliday junction resolvases (HJR) which have been identified in a wide variety of organisms based on their shared biochemical characteristics. Bioinformatics analyses of the evolutionary relationships among HJ resolvases suggests that HJR function has arisen independently from four distinct structural folds, namely RNase H, endonuclease VII-colicin E, endonuclease and RusA. Furthermore, similar analyses of HJRs identified another family within the RNaseH fold, along with previously characterized RuvC family of junction resolvases. This new family of putative HJRs is typified by E. coli Yqgf protein. The yqgf gene is highly conserved among bacterial genomes. Nuclear magnetic resonance structural studies have disclosed notable structural similarities between E. coli RuvC and YqgF proteins. Utilizing homology-based molecular modelling, YqgF is predicted to function as a nuclease in various aspects of nucleic acid metabolism. Sequence analysis of M. tuberculosis genome has revealed the presence of two putative HJ resolvases, ruvC (Rv2594c) and ruvX (Rv2554c, yqgF homolog). Previous studies have demonstrated that M. tuberculosis ruvC is induced following DNA damage and ruvX is expressed during active growth phase of M. tuberculosis. More importantly, the absence of ruvC increased the potency of moxifloxacin in M. smegmatis. Although, these results imply that the ruv genes play crucial roles in DNA recombination and repair in M. tuberculosis, the biochemical properties of their gene products have not been characterized. In this study, we have isolated M. tuberculosis ruvC and yqgF genes and purified their encoded proteins, M. tuberculosis RuvC (MtRuvC) and M. tuberculosis RuvX (MtRuvX), respectively, to near homogeneity. Protein-DNA interaction assays conducted with purified MtRuvC and MtRuvX revealed that both can bind HJ, albeit with different affinities. However, in contrast to MtRuvC, MtRuvX showed robust HJ resolvase activity. The endonuclease activity of MtRuvX was completely dependent on Mg2+and Mn2+ partially substituted for Mg2+. Additional experiments showed that RuvX exhibits >2-fold higher binding affinity for HJ over other recombination/ replication intermediates. As demonstrated for other HJRs, MtRuvX failed to cleave static HJ and linear duplex DNA. The cleavage sites were mapped within the homologous core of a branch-migratable HJ. To identify catalytic residues in RuvX, we conducted mutational analysis of an acidic amino acid residue guided by the bioinformatics data. The product of MtRuvXD28N retained full HJ-binding activity, but showed extremely reduced HJ-specific endonuclease activity. Further biochemical characterization revealed that MtRuvX exists as a homodimer in solution. Notably, we found that disulfide-bond mediated intermolecular homodimerization is crucial for the ability of MtRuvX to cleave Holliday junctions, implicating that stable junction binding is necessary to promote branch migration and to create cleavable sites. Analysis of qPCR data suggested that the pattern of yqgF gene expression was similar to those of ruvC and recA genes following DNA damage. Together, these data indicate that ruvX expression is induced by DNA-damaging agents and that RuvX might be functionally involved in recombinational DNA repair in M. tuberculosis. These findings are all consistent with the idea that RuvX might be the bona fide HJ resolvase in M. tuberculosis analogous to that of E. coli RuvC. More importantly, we provide the first detailed characterization of RuvX and present important insights into the mechanism of HJ resolution, which could be directly linked to the regulation of different DNA metabolic processes, including HR, DNA replication and DNA repair. Overall, this study opens a new avenue in the understanding of HR in this human pathogen, together with elucidation of the function of some of the uncharacterized genes may represent a novel set of recombination enzymes.

42

Nautiyal, Astha. "Understanding the Mechanism of Homologous Recombination in Mycobacterium Tuberculosis : Exploring RecA as an Antibacterial Target and Characterization of Holliday Junction Resolvases". Thesis, 2015. http://etd.iisc.ernet.in/2005/3926.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Homologous recombination (HR) is conserved across all three domains of life and is associated with a number of key biological processes. Over the years, numerous genetic, biochemical and structural studies have uncovered important mechanistic details and established a role for HR in DNA damage repair, control of DNA replication fidelity and suppression of various types of cancer. Much of our current understanding of the mechanistic aspects of HR is gained from the study of Escherichia coli paradigm. E. coli RecA is the founding member of a nearly ubiquitous family of multifunctional proteins and is substantially conserved among eubacterial species. During HR, RecA protein promotes homologous pairing followed by strand exchange reaction leading to heteroduplex formation. In addition to HR, RecA is a central component of SOS response, recombinational DNA repair and rescue of collapsed replications forks. Moreover, recent work has suggested that DNA recombination/repair mechanisms might contribute to genome evolution and consequently to the generation of multidrug-resistant strains of the pathogen. The disease caused by Mycobacterium tuberculosis, endemic in certain regions of the world, is a leading cause of disability and death. A thorough knowledge of the function and interaction of specific HR proteins/enzymes involved in the maintenance of genome integrity is essential in order to elucidate the impact of genome perturbation effects on M. tuberculosis. Toward this end, modulation of RecA protein activity, a central component of HR, represents a potential novel target for design of new drugs because of its involvement in various processes of DNA metabolism. Additionally, small molecule modulators of RecA activity may offer novel insights into the regulation and its role in cellular physiology and pathology. Traditionally, antibiotics have been used to treat infections caused by bacteria. Despite their importance, the development of new antibiotics against M. tuberculosis has considerably decreased over the past several years due to disappointing results in clinical trials. These failures may be due the fact that they suffer from low potency or low cell permeability. Therefore, one of the aims of studies described in this thesis was to test the effect of suramin, a known inhibitor of E. coli RecA, on various biochemical activities of mycobacterial RecA proteins and determine its mechanism of action. Furthermore, the most crucial step in the HR pathway and rescue of collapsed DNA replication forks is the resolution of Holliday junctions and other branched intermediates. Because Holliday junction resolvases are essential for the resolution of different types of DNA recombination/repair intermediates, therefore, we considered it worthwhile to study the genomic expression and biochemical properties of HJRs in M. tuberculosis. Suramin is a commonly used antitrypanosomal and antifiliarial drug, and a novel experimental agent for the treatment of several cancers. A forward chemical screen assay identified several small molecule inhibitors of E. coli RecA. In this screen, suramin (also called germanin), a polysulfonated naphthylurea, and suramin-like agents were found to inhibit EcRecA catalyzed ATPase and DNA strand exchange activity. However, the mechanism underlying such inhibitory action of suramin and whether it can exert antibacterial activity under in vivo conditions remains largely unknown. In an attempt to delineate the range of suramin action, we reasoned that it might be useful to test its effect on mycobacterium RecA proteins. We found that suramin is a potent inhibitor of all known biochemical activities of mycobacterial RecA proteins with IC50 values in the low μM range. The mechanism of action involves, in part, its ability to disassemble the nucleoprotein filaments of RecA-ssDNA. To validate the above results and to obtain quantitative data, a pull-down assay was developed to assess the effect of suramin on RecA–ssDNA filaments. The data indicated that suramin was able to dissociate >80% of RecA bound to ssDNA. Altogether, these results indicated the effectiveness of suramin in the disassembly of RecA nucleoprotein filament. Next, we sought to test whether suramin binds to RecA by using a CD spectropolarimeter. Significant spectral changes were observed upon addition of increasing concentrations of suramin, indicating alterations in the secondary structure of RecA protein. Additional evidence revealed that suramin impaired RecA catalyzed proteolytic cleavage of LexA repressor and blocked ciprofloxacin-inducible recA gene expression and SOS response. More importantly, suramin potentiated the cidal action of ciprofloxacin and reduced the growth of Mycobacterium smegmatis recA+ strain but not its isogenic recA∆ mutant, consistent with the idea that it acts directly on RecA protein. This approach, which appears as an appealing concept, opens up new possibilities to chemically disrupt the pathways controlled by RecA and treat drug-sensitive as well as drug-resistant strains of M. tuberculosis for better infection control and the development of new therapies. The annotated genome sequence of M. tuberculosis revealed the presence of putative homologues of E. coli DNA recombination/repair genes. However, it is unknown whether these putative genes have the ability to encode catalytically active proteins or participate in biochemical reactions intrinsic to the process of HR or DNA repair. Studies in the second half of the thesis originated from an in silico analysis for genes that encode functional equivalents of E. coli RuvC HJ resolvase(s) in M. tuberculosis. The central intermediate formed during mitotic and meiotic recombination is a four-way DNA junction, also known as the Holliday junction (HJ), and its efficient resolution is essential for proper segregation of chromosomes. The resolution of HJ is mediated by a group of structure specific endonucleases known as the Holliday junction resolvases (HJR) which have been identified in a wide variety of organisms based on their shared biochemical characteristics. Bioinformatics analyses of the evolutionary relationships among HJ resolvases suggests that HJR function has arisen independently from four distinct structural folds, namely RNase H, endonuclease VII-colicin E, endonuclease and RusA. Furthermore, similar analyses of HJRs identified another family within the RNaseH fold, along with previously characterized RuvC family of junction resolvases. This new family of putative HJRs is typified by E. coli Yqgf protein. The yqgf gene is highly conserved among bacterial genomes. Nuclear magnetic resonance structural studies have disclosed notable structural similarities between E. coli RuvC and YqgF proteins. Utilizing homology-based molecular modelling, YqgF is predicted to function as a nuclease in various aspects of nucleic acid metabolism. Sequence analysis of M. tuberculosis genome has revealed the presence of two putative HJ resolvases, ruvC (Rv2594c) and ruvX (Rv2554c, yqgF homolog). Previous studies have demonstrated that M. tuberculosis ruvC is induced following DNA damage and ruvX is expressed during active growth phase of M. tuberculosis. More importantly, the absence of ruvC increased the potency of moxifloxacin in M. smegmatis. Although, these results imply that the ruv genes play crucial roles in DNA recombination and repair in M. tuberculosis, the biochemical properties of their gene products have not been characterized. In this study, we have isolated M. tuberculosis ruvC and yqgF genes and purified their encoded proteins, M. tuberculosis RuvC (MtRuvC) and M. tuberculosis RuvX (MtRuvX), respectively, to near homogeneity. Protein-DNA interaction assays conducted with purified MtRuvC and MtRuvX revealed that both can bind HJ, albeit with different affinities. However, in contrast to MtRuvC, MtRuvX showed robust HJ resolvase activity. The endonuclease activity of MtRuvX was completely dependent on Mg2+and Mn2+ partially substituted for Mg2+. Additional experiments showed that RuvX exhibits >2-fold higher binding affinity for HJ over other recombination/ replication intermediates. As demonstrated for other HJRs, MtRuvX failed to cleave static HJ and linear duplex DNA. The cleavage sites were mapped within the homologous core of a branch-migratable HJ. To identify catalytic residues in RuvX, we conducted mutational analysis of an acidic amino acid residue guided by the bioinformatics data. The product of MtRuvXD28N retained full HJ-binding activity, but showed extremely reduced HJ-specific endonuclease activity. Further biochemical characterization revealed that MtRuvX exists as a homodimer in solution. Notably, we found that disulfide-bond mediated intermolecular homodimerization is crucial for the ability of MtRuvX to cleave Holliday junctions, implicating that stable junction binding is necessary to promote branch migration and to create cleavable sites. Analysis of qPCR data suggested that the pattern of yqgF gene expression was similar to those of ruvC and recA genes following DNA damage. Together, these data indicate that ruvX expression is induced by DNA-damaging agents and that RuvX might be functionally involved in recombinational DNA repair in M. tuberculosis. These findings are all consistent with the idea that RuvX might be the bona fide HJ resolvase in M. tuberculosis analogous to that of E. coli RuvC. More importantly, we provide the first detailed characterization of RuvX and present important insights into the mechanism of HJ resolution, which could be directly linked to the regulation of different DNA metabolic processes, including HR, DNA replication and DNA repair. Overall, this study opens a new avenue in the understanding of HR in this human pathogen, together with elucidation of the function of some of the uncharacterized genes may represent a novel set of recombination enzymes.

43

Kung, Shao-Kai, e 宮紹凱. "The preliminary study of antibacterial mechanism of low molecular weight chitosan by using differentially susceptible strains of Staphylococcus aureus and Escherichia coli". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/60560712726631128433.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

碩士
國立宜蘭大學
生物技術研究所碩士班
96
Chitin, chitosan and chitosan hydrolysates possess histocompatibility and biological activity, in addition, they have been widely applied in the biotechnology, biomedical, pharmacological and agricultural fields recently. In this study, the low molecular weight chitosans (LMWCs) were prepared by using crude chitinase (induced from Trichoderma viride), commercial lysozyme and cellulase. Due to these enzymes have different hydrolysis mechanism on chitosan with different DD, a diverse characteristics of LMWC including Mw, antibacterial activity, solubility, zeta potential could prepared from DD of 80 and 92%. The intrinsic viscosity molecular weight (MV) of LMWC form each of the combination was decreased steeply in 24 hours (from 370 kDa to 13-37 kDa) and, the order of MV were DD92_lys (24.8 kDa), DD80_lys (14.8 kDa), DD92_chit (13.5 kDa), DD80_chit (9.6 kDa), DD80_cel (8.1 kDa) and DD92_cel (6.9 kDa). The solubility of LMWC was affected strongly by Mw but not the enzyme by which LMWC was prepared. The minimum inhibition concentration (MIC) of LMWC was done by 96 microplate method. The results show that LMWC_lys has better antibacterial activity and poor solubility; in opposition, LMWC_cel had better solubility but ineffective antibacterial activity. The LMWC made from DD92 and chitinase had high solubility and good antibacterial activity. Therefore, the LMWC_DD92_chit was used for the following antibacterial activity study. The antibacterial activity test performed by using biophotorecorder method against three strains of S. aureus (BCRC 10451, 10780, 10781) and two strains of E. coli (BCRC 10314, 10675) revealed that various strains of antibacterial action of bacteria had different susceptibility to LMWC. The antimicrobial action of LMWC was strongly related to zeta potential. The more charge disparity between positive LMWC and negative bacteria, the more adsorptive power between each other, which led to higher antibacterial activity. SEM was used to observe the interaction between LMWC and the most sensitive strains S. aureus (BCRC 10451) and E. coli (BCRC 10314), and results revealed bacteria were heavily coated with LMWC. While the LMWC coat was washed away with acetic buffer, the surface integrity of bacteria was destroyed which resulted in the membrane poration on the surface. The bacterial DNA extraction analysis showed that DNA of BCRC 10780 was the most difficult to be extracted. It suggested that cell wall of BCRC 10780 was thicker, more rigid and not easy to be destroyed. In the early stage, the surface covering of LMWC can possibly cease cell division by charge neutralization. It could also invade into and cause deterioration of cell wall which leads bacteria to death.

44

Li, Liao. "Chemical Forays of Fungal Metabolites". Phd thesis, 2018. http://hdl.handle.net/1885/148782.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

This thesis contains six chapters and the research presented within focuses on three parts. The first part (chapter one to three) was the isolation of antibacterial and antioxidant mushroom metabolites, and the synthesis towards analogues of discovered natural products. The following part (chapter four) was to assess antioxidant activities of synthetic compounds and investigate their SAR (structure-activity relationship), by use of a developed DPPH assay. The last part (chapter five to six) was the discovery of an abiotic halogenation reaction among a class of fungal metabolites, azaphilones. A series of their synthetic analogues were applied as model compounds to understand the mechanism of the discovered unusual and facile non-enzymatic nucleophilic halogenation reaction. Chapter one is a review of antioxidants in mushrooms. The components with antioxidant activities discovered from mushrooms were summarised by their chemical structures and representative samples were listed. In addition, the potential mechanisms of those antioxidants were described in this chapter. In chapter two, extracts of 20 mushrooms from PNG (Papua New Guinea) were screened against both Gram-positive and Gram-negative bacteria, six of them were chosen as chemical survey candidates for their strong antibacterial activities. Extracts of 37 PNG mushrooms were screened for their antioxidant using a modified DPPH assay, 14 of them were chosen as chemical survey candidates based on their antioxidant capacities. In chemical examination guided by bioactivity, five natural products including two novel furan fatty acids (2.1-2.2) and three known compounds, i.e. grifolin (2.3), grifolic acid (2.4) and grifolic acid methyl ether (2.5), were isolated from four selected mushroom samples. Chapter three described the synthetic efforts towards analogues of three isolated antioxidant fungal metabolites (2.3-2.5). Inspired by 15 synthetic targets, a short and versatile general synthetic route was established to deliver 40 compounds possessing structures related to the natural products. Based on these structures, a compound library was established for antioxidant assessment in the following SAR research. The synthetic work resulted in the preparation of 33 novel structures. In chapter four, various antioxidant assays and their working mechanisms were reviewed, as well as their corresponding advantages and drawbacks. A developed DPPH assay was optimised to offer an accurate and reproducible antioxidant evaluation for SAR research in the achieved compound library. The results indicated that a structure with an aromatic ring to be allylated with a carbon chain in addition to the presence of phenols, is required to show an antioxidant activity, and the increased length of a carbon chain (more prenyl units) enhances the antioxidant activity. Chapter five focused on naturally occurring organohalogen compounds with biotic origins. The representative halogenated natural products with a variety of bioactivities were categorised following a chemical structural classification as well as a bioactive classification, to showcase both their structural diversity and bioactive variety. The biosynthetic mechanisms of halogenated natural products were reviewed in this chapter. Chapter six detailed the investigation of a novel halogenation reaction that was discovered to be occurring with some azaphilone fungal metabolites, for example the conversion of (+)-deschlorosclerotiorin (6.2) into (+)-sclerotiorin (6.1). Various non-halogenated model compounds with an azaphilone core structure were created to shed light on the authenticity of numerous halogenated azaphilones reported as natural products. The ensuing synthetic work resulted in an efficient general procedure producing the required targets. The following investigation of the halogenation revealed a novel, facile, non-enzymatic nucleophilic reaction and its proposed mechanism is discussed. The synthetic efforts resulted in the creation of 22 novel structures.

45

Lin, Siou-Hong, e 林秀鴻. "Antibacterial mechanisms of the nanohybrid of the immobilized silver nanoparticles and exfoliated platelet clay". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/67414381473069993205.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

碩士
國立中興大學
生命科學系所
98
Silver is well known for its antimicrobial activity. Due to the extraordinary antibacterial activity, silver and its compound are widely used in medical filed such as wound healing and burns infections. The antibacterial mechanisms of silver ions that dissociated from silver compounds have been studied by many researchers. For instance, silver ions that dissociated from silver nitrate disrupt normal cell function and inhibit cell growth by binding with thiol group in protein. Recent years, nanotechnology developed prosperously. Nano is 10-9 or billionth of one meter. Silver nanoparticles were synthesis for the advantage of its antibacterial activity and low cytotoxicity to eukaryotic cells. The antibacterial activity of silver nanoparticles against broad-spectrum strain of bacteria has been studied, including gram-positive, gram-negative, fungi and even HIV virus. In this study, we have used a novel nanohybrid that consisted of silver nanoparticles and exfoliated nature silicate clay (AgNP/NSP). Silicate clay served as disperse for silver ions in situ reduced into immobilized silver nanoparticeles. To elucidate the antibacterial mechanisms of this nanocomposite, several experiments were applied. FE-SEM observation revealed the morphology of AgNP/NSP treated cells. Reactive oxygen species (ROS) detecting assay indicated the generation of ROS may be the major contributor for the cell membrane damage consistent with the result of Live/Dead assay that AgNP/NSP post-treated cells were dead. And according to the result of free radicals scavengers blocking ROS generation experiment, we can speculate that ROS is mainly result in lipidperoxidation leading to cell membrane damage and cell death. A strong antioxidant glutathione rescued bacteria cells survival rate from AgNP/NSP containing plates also a result consistent with above hypothesis. We also demonstrated that the glucose uptake of cells was diminished by treating AgNP/NSP. The intracellular ATP level of AgNP/NSP post-treated cells also decreased. These results indicat that AgNP/NSP hinder the normal cell physiological function such as metabolism and energy production. In this study, we have elucidated the mechanisms of AgNP/NSP and hope it will be helpful for future design of safer and more sophisticated antibacterial materials.

46

蘇亞玫. "Affecting factors and mechanisms of the antibacterial activities of chitosan with various molecular weights". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/43732174766256501764.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

47

Monteiro, Pedro Manuel Duarte. "Fighting the resistance: algae as key organisms against antibacterial resistance". Master's thesis, 2020. http://hdl.handle.net/10316/93951.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Dissertação de Mestrado em Biologia Celular e Molecular apresentada à Faculdade de Ciências e Tecnologia
A resistência bacteriana é um dos problemas de saúde pública do século XXI. No geral, o abuso e consumo de antibacterianos nos diversos setores, como o cultivo, agricultura e cuidados de saúde, promoveu a resistência de bactérias a praticamente todos os compostos antibacterianos disponíveis no mercado. Além dos mecanismos de resistência, amplificados a partir da pressão seletiva constante deste consumo exacerbado (por exemplo, bombas de efluxo, alteração mutacional do alvo e inibição enzimática do agente antibiótico), o desafio imposto por infeções relacionadas com formação de biofilmes, caracterizado por forte recalcitrância, requer soluções alternativas na exploração e desenvolvimento de novos agentes terapêuticos. Os compostos bioativos isolados de ambientes aquáticos (marinhos ou de água doce), macro- e microalgas, apresentam grande potencial terapêutico, devido à sua variabilidade de compostos, que se apresentam como novos agentes antibióticos alternativos. Os metabólitos primários e secundários produzidos por esses organismos apresentam uma miríade de propriedades bioativas com reconhecido potencial para serem introduzidos no mercado comercial. No entanto, a variabilidade inerente desses organismos e consequente variabilidade na extração é um sério desafio para a padronização dos métodos de extração, etapa essencial na transferência de tecnologia para o setor industrial. Este trabalho apresenta uma visão geral dos desafios atuais na resistência bacteriana, como a utilização de antibióticos em ambiente antropogénico e mecanismos de resistência, com uma exploração mais profunda da ecologia da estrutura de biofilmes e a sua ligação à infeção e resistência à terapêutica. Além disso, são apresentados compostos bioativos encontrados em algas, com discussão dos seus efeitos antibacterianos e o desafio da transferência desta tecnologia e conhecimento do laboratório para o ambiente industrial e comercial
Antibacterial resistance (ABR) is one of the public health problems of the XXI century. Overall, abuse in use and consumption of antibacterials in several sectors, such as crops, agriculture and healthcare, has promoted bacterial resistance to practically all therapeutic compounds available in market. Apart from conventional resistance methods, amplifyed from the constant selective pressure (e.g. efflux pumps, mutational alteration of target of enzymatic inhibition of antibiotic agent), the challenge imposed by biofilm-related infections, characterized by strong recalcitrance, requires alternative solutions in exploration and developing of new therapeutic agents. Bioactive compounds isolated from aquatic (marine or freshwater), from macro- and microalgae species, contain great potential in compound variability, that hold future as new alternative antibiotic agents. The primary and secondary metabolites produced by these organisms show a myriad of bioactive properties with recognized potential to be introduced in the commercial market. However, inherent variability of these organisms and compounds produced are a serious challenge for extraction standardization, an essential step in the transference of technology to the industrial sector. This work overviews current challenges in global bacterial resistance, such as anthropological antibiotic uses and bacterial mechanisms of resistance, with deeper exploration of bacterial biofilm ecology and connection to infection and therapeutic resistance. Additionally, it is examined bioactive compounds present in algae, with discussion of their antibacterial effects and the challenge of technological transference from the laboratory to the industrial and commercial setting.

48

Yu-HsuanShih e 史育璇. "Antibacterial effects and the mechanisms of stilbenoid compounds alone or combined with silver nanoparticles against foodborne pathogens". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/p5j4c4.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

49

(5930066), Jesus Hector Morales Espejo. "Antimicrobial Peptide Adsorption and Storage on Oxidized Metal Surfaces to Mitigate Bacterial Attachment". Thesis, 2018.

Cerca il testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

In the pursuit to create more natural, chemical-free antibacterial surfaces, fracture mechanics and the ability of laser-modified surfaces to store an antimicrobial agent have been investigated through the combination of scanning electron microscopy coupled with focused ion beam, infrared spectroscopy, bactericidal tests and a colorimetric method. It was found that the irradiation of a nanosecond pulsed laser on Ti-6Al-4V and 304L stainless steel surfaces creates colored oxide layers with 100-150 nm in thickness and, by using the adequate parameters, it is possible to obtain surfaces with cracks of 1-6 μm deep that not only penetrate the film but also the substrate. Physisorption was used to immobilize nisin, an antimicrobial agent, to the walls of those cracks. Antibacterial tests show that nisin-coated oxide layers exhibit antibacterial activity against Listeria monocytogenes even after immersion in water or the application of mechanical scrubbing, and release kinetics tests demonstrated that nisin desorption is promoted by acidic pH and that nisin is effectively stored into the cracks of stainless steel. The immobilization into the cracks of the titanium oxide layer seem to reveal that there is an excellent anchor between the peptide and the crack walls, but future research is still required.

50

Ghosh, Somnath. "Investigation On Ag And ZnO Based Nanohybrids As Bactericides For The Purification Of Water And Elucidation Of Possible Mechanisms For Their Bio-activity". Thesis, 2012. https://etd.iisc.ac.in/handle/2005/2492.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Chapter I: This chapter briefly gives an introduction about microorganisms, their varieties, growth, reproduction etc. In particular, about bacterial function. A sincere attempt is made to review this briefly, including an account of the studies already reported in the literature. Chapter II deals with the antimicrobial activity of Ag/agar film on Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Candida albicans (C. albicans). In particular, films were repeatedly cycled for its antimicrobial activity. The antimicrobial activity of Ag/agar film was found to be in the order, C. albicans > E. coli > S. aureus. Chapter III describes the synthesis of Ag@AgI NPs in agarose matrix. A detailed antibacterial studies including repetitive cycles are carried out on E. coli and S. aureus bacteria. EPR and TEM studies are carried out on the Ag@AgI/Agarose and the bacteria, respectively, to elucidate a possible mechanism for killing of the bacteria. The hybrid could be recycled for the antibacterial activity many times and is found to be non toxic towards human cervical cancer cell (HeLa cells). Chapter IV reports the antibacterial efficacy of silver nanoparticles (Ag NPs) deposited alternatively layer by layer (LBL) on chitosan polymer in the form of a thin film over a quartz plate and stainless steel strip against E. coli. AFM studies are carried out on the microbe to know the morphological changes affected by the hybrid film. The hybrid films on aging (3 months) are found to be as bioactive as before. Cytotoxicity experiments indicated good biocompatibility. Chapter V describes the fabrication of carbon foam porous electrode modified with reduced graphene oxide-Ag nanocomposites. The device can perform sterilization by killing pathogenic microbes with the aid of just one 1.5V battery with very little power consumption. Chapter VI Here we have studied in particular a property say the influence of surface defect in the production of ROS by ZnO NPs and in turn the bactericide activity. Secondly, a homogeneous ZnO and ZnO/Ag nanohybrid has been synthesized by employing chitosan as mediator. The synergistic antibacterial effect of ZnO/Ag nanohybrid on bacteria is found to be more effective, compared to the individual components (ZnO and Ag). A possible mechanism has been proposed for the death of bacteria by ZnO/Ag nanohybrid, based on EPR studies and TEM studies.

Tesi sul tema "Antibacterial mechanism"

Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili