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Tesi sul tema "Pathogens"
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1
Hovhannisyan, Hrant 1992. "Comparative transcriptomics of host-pathogen interactions and hybridization in Candida pathogens". Doctoral thesis, Universitat Pompeu Fabra, 2020. http://hdl.handle.net/10803/670316.
Testo completoAbstract (sommario):
Candida pathogenic yeasts represent a global healthcare problem. They comprise phylogenetically diverse species, including newly emerged pathogens. How human-Candida interactions vary across species, and what processes underlie the emergence of novel pathogens are poorly understood. Current thesis addresses these issues using comparative transcriptomics and bioinformatics. We established the global patterns of host-pathogen interactions between human host and the main Candida species, providing novel mechanistic insights into their interplay. We also explored lncRNAs of these pathogens, assessing their implications in infection. Further, we designed and validated a pan-Candida RNA enrichment approach, opening new possibilities for studying host-pathogen interactions in vivo. Then, we assessed the impact of hybridization on transcriptomes of hybrid yeasts, exploring the links between hybridization and virulence emergence. We also developed a new bioinformatics tool facilitating the research in the field. Altogether, results of this thesis expand our knowledge on relevant aspects of human-Candida interactions and yeast evolution.Las levaduras patógenas Candida representan un problema de salud global. Este grupo de levaduras, comprenden especies filogenéticamente diversas, e incluye patógenos emergidos recientemente. La forma en que las interacciones entre humanos y Candida varían de una especie a otra y qué procesos subyacen a la aparición de nuevos patógenos son poco conocidos. La tesis actual aborda estos problemas utilizando una aproximación de transcriptómica comparativa y bioinformática. Establecimos los patrones globales de las interacciones huésped-patógeno entre el huésped humano y las principales especies de Candida, proporcionando nuevas ideas mecanicistas sobre su interacción. También exploramos los lncRNA de estos patógenos, evaluando sus implicaciones en la infección. Además, diseñamos y validamos un enfoque de enriquecimiento de ARN pan-Candida, abriendo nuevas posibilidades para estudiar las interacciones huésped-patógeno in vivo. Luego, evaluamos el impacto de la hibridación en los transcriptomas de levaduras híbridas, explorando los vínculos entre la hibridación y la aparición de virulencia. En su conjunto, los resultados de esta tesis amplían nuestro conocimiento sobre aspectos relevantes de las interacciones humano-Candida y la evolución de las levaduras.
2
Kärkkäinen, Riikka M. "Production of DNA aptamers with specificity for bacterial food pathogens". Thesis, University of Chester, 2012. http://hdl.handle.net/10034/620695.
Testo completoAbstract (sommario):
Aptamers are biomolecular ligands composed of nucleic acids. They can be selected to bind specifically to a range of target molecules and subsequently exploited in a fashion analogous to more traditional biomolecules such as antibodies. In this study a method for selecting new aptamers which specifically bind whole live bacterial cells is described. A non-pathogenic strain of Escherichia coli K12 was used to develop the method. A DNA library containing 100 bases long random nucleotide sequences was produced and the aptamer selection process was repeated nine times. An enzyme-linked technique was first used to detect bound aptamers thereafter fluorimetry and fluorescence microscopy methods were used for the detection. The aptamers were cloned and sequenced and the cloned aptamers produced with fluorescent labels. The E. coli K12-binding aptamers were used to demonstrate the detection of the bacterial cells in a complex food matrix, namely probiotic yogurt, by using fluorescence based detection method. The aptamer selection method with some modifications was also used to select aptamers with specificity for the food pathogens E. coli O157, Listeria monocytogenes, L. innocua, S. typhimurium and S. enteritidis. The aptamers against E. coli O157 and S. typhimurium were cloned and the sequences and the binding properties of these aptamers were analysed. The use of E. coli K12 as a target organism and the aptamer sequences presented in this study, have not previously been published in scientific literature. This is also the first report where the aptamers have been used in detection of live bacterial cells in yogurt.
3
Gibson, Josie. "In vivo imaging and analysis of host-pathogen interactions of intracellular pathogens". Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/19047/.
Testo completoAbstract (sommario):
Cellular and extracellular host-pathogen interactions are important in the progression of infection. Extracellular survival and growth can be significant for pathogen dissemination. Equally, intracellular pathways, such as autophagy, can be employed in host cell defence. Autophagy is a cellular self-degradation process that recycles cellular components through lysosomal degradation. Primarily for regulating starvation and housekeeping pathways, autophagy is also important for degradation of invading intracellular pathogens. Selective autophagy receptors can also target pathogens for autophagic degradation. However, some intracellular pathogens are able to subvert or block host cell autophagy. Cryptococcus neoformans and Staphylococcus aureus represent fungal and bacterial pathogens which can reside either intracellularly or extracellularly. The role of host cell autophagy in C. neoformans and S. aureus infection is unclear. Infection of zebrafish with C. neoformans or S. aureus enabled in vivo imaging of host-pathogen interactions, to examine infection growth dynamics and dissemination, in addition to cellular level imaging of pathogen interactions with host cell autophagy components. Cryptococcal infection can cause cryptococcal meningitis, frequently associated with cerebral infarcts. Analysis of cryptococcal proliferation during infection suggested that formation of intravascular cryptococcal masses precedes invasion of surrounding tissue. Vessel integrity analysis highlighted cryptococcal-mediated vascular damage, potentially providing a route for tissue dissemination. Vasculature damage may explain the origin of cortical infarcts in disease. Autophagy mutant zebrafish were generated to analyse host autophagy in pathogen infection. Characterisation of mutant larvae revealed a clear survival and growth defect, indicating autophagy is required for larval development. Autophagy mutants were subsequently used to analyse the role of autophagy during infection through analysis of pathogenic burden and pathogen association with autophagosome marker LC3-II. LC3II recruitment to pathogens was reduced in autophagy mutant neutrophils. Additionally, selective autophagy receptor p62 was recruited to S. aureus and C. neoformans within neutrophils, highlighting the involvement of host cell autophagy during infection.
4
Jones, Steven Michael. "Nosocomial pathogens within biofilms". Thesis, University of Exeter, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370017.
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5
Ahmad, Sarah. "Identification of pathogen-specific protein-encoding genes from microbial pathogens based on bioinformatic analysis". Thesis, University of Exeter, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425246.
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6
Sousa, Oliveira Márcia Patrícia de. "Microbial safety of lettuce: foodborne pathogens incidence, their pathogenic potential and biopreservative stratagies". Doctoral thesis, Universitat de Lleida, 2015. http://hdl.handle.net/10803/307379.
Testo completoAbstract (sommario):
La investigació descrita en aquesta tesi es centra en la determinació de la influència de les pràctiques de maneig del cultiu, processament i les condicions d'emmagatzematge en la qualitat microbiològica de l'enciam mínimament processat i en l'estudi de les estratègies de mitigació per millorar la seva seguretat. S'ha estudiat l'efecte del sistema de producció, orgànica o convencional, de la qualitat microbiològica d'enciam fresc. Es va avaluar la transferència i la persistència de L. innocua i E. coli O157:H7 en els fulls d'enciam i en el sòl durant la tardor i la primavera utilitzant diferents mètodes de reg contaminats artificialment i el compost. La capacitat de L. monocytogenes, Salmonella i E. coli O157:H7 per créixer en enciam envasat en tres condicions d'atmosfera diferents creades per mitjà de la utilització de pel•lícules de diferents permeabilitats a dues temperatures d'emmagatzematge va ser evaluada. Es va examinar el potencial patogènic de dues soques de S. Typhimurium DT104, amb l'objectiu de mesurar la seva capacitat per sobreviure al tracte gastrointestinal simulat i d'adherir i envair cèl•lules diferenciades Caco-2, després d’una incubació seqüencial al sòl, l'enciam i enciam tallat emmagatzemat en condicions de MAP. En aquesta tesi l'efecte de millorar la microbiota d'enciam sotmesa a les diferents etapes de pre-condicionament en la supervivència de L. monocytogenes i E. coli O157:H7 com a mètode bioconservant també va ser avaluat. Finalment, s'ha estudiat l'ús de l'addició de bioconservants com a mètode per a controlar o reduir PTA en enciam mínimament processada.La investigación descrita en esta tesis se enfoca en la determinación de la influencia de las prácticas de manejo del cultivo, procesamiento y condiciones de almacenamiento en la calidad microbiológica de la lechuga mínimamente procesada y en el estudio de las estrategias de mitigación para mejorar su seguridad. Se ha estudiado el efecto de los sistemas de producción, orgánico o convencional, en la calidad microbiológica de lechuga fresca. Se evaluó la transferencia y la persistencia de L. innocua y E. coli O157:H7 en las hojas de lechuga y en el suelo durante el otoño y la primavera, utilizando diferentes métodos de riego contaminado artificialmente y el compost. La capacidad de L. monocytogenes, Salmonella y E. coli O157:H7 para crecer en lechuga mínimamente procesada y envasada en tres diferentes condiciones de atmósfera, creada por la utilización de películas con diferentes permeabilidades a dos temperaturas de almacenamiento fue evaluada. Se examinó el potencial patogénico de dos cepas de S. Typhimurium DT104, con el objetivo de medir su capacidad para sobrevivir al tracto gastrointestinal simulado y de adherirse e invadir a las células diferenciadas Caco-2, después de la incubación secuencial en el suelo, lechuga y lechuga cortada almacenada en MAP. En esta tesis también se evaluó el efecto de aumentar la microbiota de lechuga sometida a las diferentes etapas de pre-acondicionamiento en la supervivencia de L. monocytogenes y E. coli O157:H7 como método bioconservante. Por último, se ha estudiado el uso de la adición de bioconservantes como método para controlar o reducir los PTA en lechuga mínimamente procesada.
The research described in this thesis is focused on the determination of the influence of field management practices, processing and storage conditions on the microbial quality of fresh-cut lettuce and on the study of mitigation strategies to enhance its safety. The effect of production system, organic or conventional, on the microbiological quality of fresh lettuce was studied. The transfer and persistence of L. innocua and E. coli O157:H7 on lettuce leaves and in soil during fall and spring using different artificially contaminated irrigation methods and compost was evaluated. The ability of L. monocytogenes, Salmonella and E. coli O157:H7 to grow on shredded lettuce packaged in three different atmosphere conditions created by means of using different permeability films at two storage temperatures was evaluated. The pathogenic potential of two S. Typhimurium DT104 strains was examined, with the aim to measure their capability to survive a simulated gastrointestinal tract system and to adhere to and invade differentiated Caco-2 cells, after sequential incubation into soil, lettuce and cut lettuce stored under MAP conditions. In this thesis the effect of enhancing native microbiota of lettuce submitted to different pre-conditioning steps on survival of L. monocytogenes and E. coli O157:H7 as a biopreservative method was also evaluated. Finally, the use of adding biopreservatives as a method to control or reduce FBP in fresh-cut lettuce was studied.
7
Mixão, Verónica de Pinho 1991. "Hybridization in Candida yeast pathogens". Doctoral thesis, Universitat Pompeu Fabra, 2020. http://hdl.handle.net/10803/670103.
Testo completoAbstract (sommario):
Candida species are among the most important fungal pathogens. Although Candida albicans is the most common cause of Candida infections, many other Candida species have emerged as pathogens. How pathogenicity is evolutionary acquired is unknown, but previous studies point to a role of hybridization in its development. This thesis studied the genomic features of Candida pathogens, with a special focus on hybrids and their evolution. Specifically, it asked the questions of how spread are hybrids among Candida species, and what are the processes that drive the evolution of their genomes. To this end, genomes from 141 isolates belonging to 13 Candida species were analyzed and compared, to reconstruct their features and evolution. Overall, this thesis supports an important role of hybridization in the emergence of new yeast pathogens and provides novel insights on the evolutionary aftermath of hybridization.Candida spp. se encuentran entre los hongos patógenos más importantes. Candida albicans es la principal causante de infecciones por Candida, pero muchas otras especies del mismo género han emergido como patógenos. Los mecanismos evolutivos implicados en la adquisición de patogenicidad se desconocen, pero estudios precedentes apuntan a que la hibridación puede haber jugado un papel importante en este desarrollo. Esta tesis estudia las características genómicas de las especies patógenas del género Candida, centrándose en híbridos y su evolución. Específicamente, se analiza la presencia de híbridos entre las especies de Candida y se estudian los procesos que impulsan la evolución de sus genomas. Para ello, se analizaron y compararon los genomas de 141 cepas correspondientes a 13 especies con el propósito de reconstruir sus características genómicas y estudiar su evolución. En resumen, esta tesis respalda un papel importante de la hibridación en la aparición de nuevas levaduras patógenas y aporta nuevas ideas sobre las consecuencias evolutivas de dicha hibridación.
8
Dawkins, Glenys Heather Mary. "Plant pathogens and ecological succession". Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/8317.
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9
Krüger, Carina. "Passive immunization against oral pathogens /". Stockholm, 2004. http://diss.kib.ki.se/2004/91-7349-960-9/.
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10
Encheva, Vesela. "Proteome analysis of bacterial pathogens". Thesis, University of East London, 2005. http://roar.uel.ac.uk/1301/.
Testo completoAbstract (sommario):
The explosive progress over the past decade in the fields of genomics, bioinformatics and mass spectrometry has resulted in an increased capability to investigate and compare the global protein expression of cells, tissues and organisms. The main focus of this study was on characterising the protein expression profiles of different serovars of Salmonella enterica and different serotypeso f Streptococcusp neumoniae in an attempt to identify protein factors associatedw ith host specificity and virulence. A novel approach for typing of bacterial isolates using SELDI TOF MS was developed. A thorough investigation on the effect of different factors on the quality of the SELDI profile was carried out, and the potential of several software programmes to perform cluster analysis of the SELDI data was assessedB. oth cytosolic and membrane-associatepdr oteins were separatedb y 2D GE, and detailed referencem aps of the proteins expressedu nder standardisedc. onditions were created.I n the caseo f Salmonella, it containedm ore than 300 proteins. The comparativea nalysisa t the subspeciesle vel revealedt hat, in many cases,t he variation in the expression patterns was greater between strains with the same serospecificity than betweens erotypes/serovarss, uggestingt hat the serological properties of bacteria do not correlate with differential protein synthesis. However, in the case of Salmonella, where the serovars have different host specificity, the high resolution 2D gel maps revealed several serovar-specific proteins, including enzymes involved in the catabolismo f various substrates,o r in the processo f cell detoxification. Changesi n the expression patterns of the serovars in different growth conditions, such as pH or oxygen availability, were mostly universal amongst the serovars, although a few serovar-specific proteins were also present. The findings revealed parts of the proteome that alter their expression when the microorganism are subjected to unfavourable conditions such as while colonising the host, amongst other parts that remain stable. Overall, the results demonstrated the importance of analysing many different isolates when performing protein expression studies in highly variable microbial populations.
11
McGinley, Susan. "Emerging Pathogens: Detecting Waterborne Microsporidia". College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2000. http://hdl.handle.net/10150/622275.
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12
SHAHZAD, GUL I. RAYNA. "BIOCONTROL STRATEGIES AGAINST PLANT PATHOGENS". Doctoral thesis, Università degli Studi di Milano, 2021. http://hdl.handle.net/2434/850186.
Testo completoAbstract (sommario):
It is a known fact that the whole agriculture system is suffering from the diseases caused by plant pathogens, affecting negatively the crop yield production, food security, biodiversity, agricultural ecosystem and hence agricultural economy. In many countries, the containment strategies of plant pathogens are still depending on chemical pesticides that cause adverse effects in the long term. According to the implementations reinforced by European council 2009/128/EC, biocontrol strategies are considered as the most profound and integrated approach for sustainable disease management. Defining biocontrol in terms of plant pathology, it is the purposeful utilization of beneficial microbes, or its molecules, to suppress phytopathogens’ ability to colonize or induce symptoms in the host. In spite of their lesser shelf-life and unreliability as compared to conventional pesticides, their targeted biological interaction with the phytopathogens reduces the possibility of affecting non-target organisms, environment and the development of resistance in the pathogen.
In this context, exploitation of bacterial endophytes has gained much attention during the past decades. Endophytic plant growth promoting bacteria (ePGPBs) mediate their biocontrol efficacy by targeting species through a multitude of direct or indirect biological interactions, often employing both modes of action, such as plant growth promotion, host’s resistance induction, allelochemicals secretion, and nutrients and niche competition. Another strategy that has gained popularity is the exogenous application of double stranded RNA (dsRNA), which is considered as the key trigger molecule of RNA interreference (RNAi), a post-transcriptional gene silencing mechanism, and has been shown to provide protection without the need for integration of dsRNA-expressing constructs as transgenes.
In the present doctoral thesis, the above-mentioned biocontrol strategies were adapted, utilizing “ePGPBs as microbial inoculants” and “exogenously applied dsRNA as RNAi based natural product”, against several phytopathogens belonging to different families of viruses and fungi.
Regarding ePGBPs as microbial inoculants, the objective of this study was to extend our understanding of five endophytic bacterial strains; Pantoea agglomerans (255-7), Pseudomonas syringae (260-02), Lysinibacillus fusiformis (S4C11), Paraburkholderia fungorum (R8), Paenibacillus pasadenensis (R16); that have shown a promising result in previous studies. In the present doctoral study, these strains were tested in planta to evaluate their role in providing plant growth promotion and broad-spectrum protection against two target pathosystems (viruses and fungi) that might have direct, indirect or simultaneous effects,
proceeded with two following aims: (Aim 1) action against viruses: Cymbidium ringspot virus (CymRSV), Cucumber mosaic virus (CMV), Potato virus X (PVX), and Potato virus Y (PVY) on Nicotiana benthamiana plants, comparing their effects with those of three chitosan-based products, which are known to induce resistance in plants; and (Aim 2) action against fungal pathogens: Rhizoctonia solani, Pythium ultimum and Botrytis cinerea on Lactuca sativa plants, comparing their effects with Bacillus amyloliquefaciens strain (CC2) and Trichoderma spp. based product, under controlled conditions.
To test the priming efficacy of ePGPBs against target viruses, several phenotypic parameters were observed along with the evaluation of three plant defense related genes (EDS1, PR2B and NPR1) on Nicotiana benthamiana plants. Interestingly, the symptoms reduction was successfully registered against CymRSV and CMV with increased heights of the plants. Some of the treatments were shown correlation between severity of symptoms and the virus concentration in the plants. Furthermore, the molecular interaction indicated the involvement of a salicylic acid (SA) mediated defense pathway as evidenced by the increased expression levels of EDS1 gene in strains R16 and 260-02. Whereas, strain S4C11 showed downregulation of PR2B gene, suggesting that SA-independent pathways could be involved. These findings opened queries regarding the duration of the protective effect, host-plant- pathogen interaction, and epidemiological implications of the use of similar biocontrol strains, that reduce the symptoms but not the concentration of virus in the host.
To test the ePGPBs role against target fungi (pre- and post-harvest stage), several experiments were conducted including phenotypic paraments, gene expression analysis (PR1, PAL, ThlP3, ERF1 and ACCS1), microbiota analysis in bulk soil, rhizosphere, and root associated with Lactuca sativa in the presence or absence of the inoculants, and nutritional quality parameters at time of harvest and during shelf-life of Romaine lettuce. The results were accompanied in terms of symptoms reduction by strain R16 (P. ultimum, R. solani, B. cinerea) and strain 260-02 (R. solani, B. cinerea); % seed germination by strains R16, 260-02, 255-7, S4C11 in some healthy and R. solani infected lettuce varieties; inhibition of R. solani population in soil and rhizosphere soil by strains R16, 260-02 and 255-7. Furthermore, composition of the bacterial microbiota was radically different in the rhizosphere and the root endosphere among treatments, while the bulk soil formed a single cluster regardless of treatment, indicating that the use of these treatments did not have an ecological impact outside of the plant. Also, these strains were able to contribute to the maintenance of nutritional quality indexes of lettuce at harvest and during storage. All the obtained results indicated that these
strains were involved directly (via antibiosis) and indirectly (via SA or ET/JA) in the observed reduction of symptoms. Particularly, strain R16 upregulated both PAL and ACCS1 gene in R. solani infected L. sativa (suggesting co-activation of SA- and JA/ ET mediated ISR resistance); strain 260-02 upregulated PAL gene in R. solani infected romaine lettuce and showed higher levels of ascorbic acid (AsA) production in B. cinerea infected romaine lettuce (suggesting the activation of SA- and AsA-mediated antioxidant resistance); and strain 255-7 triggered PAL and ThlP3 gene up-stream expression levels indicating SA mediated pathways in R. solani infected romaine lettuce. These findings affirmed the previous conclusions and added valuable pieces of information regarding the traits these ePGPB carried, most importantly, in individuating different mode of action of the different strains in different host plants with or without the presence of pathogen.
Regarding the second approach, non-transgenic strategy was employed to induce resistance against Tomato Aspermy Virus (TAV) in N. benthamiana plants. DsRNA molecules for coat protein (CP) gene was produced by a two-step PCR assay followed by in vitro transcription and purification and was exogenously applied. The implementation of CP-derived dsRNA TAV was not successful in reducing observed symptoms (mosaics, blisters, crinkling, leaf distortion, and systemic vein clearing), regardless of treatments or days of post inoculation. Only a slight difference was found in plant heights indicating that the treatment managed to reduce stunted growth of the plant at dilution 01:10 (6 and 12 dpi). The reasons could involve inappropriate concentration of dsRNA inoculum. Therefore, future studies will be conducted to optimize in vitro dsRNA molecules production to obtain higher concentrations or more specific sequences, and more suitable viral genes.
Both strategies have shown interesting outcomes and gave us the future direction which will help us in designing the adequate trials (in planta or semi-field) for the disease management and diseases control through the application of ePGPBs as a microbial inoculants and dsRNA-based product individually or in combination.
13
Cotter, Sheena C. "Trade-offs in insect disease resistance". Thesis, University of Stirling, 2002. http://hdl.handle.net/1893/26688.
Testo completoAbstract (sommario):
The ability to mount an efficient immune response should be an important life-history trait as parasitism can impact upon an individual's fecundity and survival prospects, and hence its fitness. However, immune function is likely to be costly as resources must be divided between many important traits. Whilst many studies have examined host resistance to particular parasite types, fewer have considered general immune responses. Studies that have considered general immune responses tend to do so in vertebrate models. However, the complexity of the vertebrate immune system makes the examination of evolutionary aspects of immune function difficult. Using larvae of the genus Spodoptera (Lepidoptera: Noctuidae) as a model system, this study examines' genetic and phenotypic aspects of innate immunity. The aims were to assess the levels of additive genetic variation maintained in immune traits, to consider possible costs that could maintain this variation, and to assess the role of phenotypic plasticity in ameliorating those costs. A key finding of this study was that high levels of additive genetic variation were maintained in all of the measured Immune traits. Analysis of the genetic correlations between traits revealed potential trade-offs within the immune system and between immune components and body condition. In addition, it was shown that larvae living at high densities invest more in immune function than those living in solitary conditions, suggesting that larvae can minimise the costs of immune function by employing them only when the risk of pathogenesis is high.
14
Almiman, Bandar F. "Molecular genetic and genomic characterization of an emerging mycotoxigenic pathogen Fusarium proliferatum". Thesis, University of Bedfordshire, 2018. http://hdl.handle.net/10547/622835.
Testo completoAbstract (sommario):
This aim of this research was to elucidate the genotypic diversity of the mycotoxigenic species Fusarium proliferatum associated with diverse hosts and distributed in wide geographic locations to gain new insights into the biology of this emerging pathogen. This study developed a novel molecular genetic marker FG1056. Multilocus typing of F. proliferatum isolates (52) using F. verticillioides (2) and F. oxysporum (3) as references was carried out with FG1056 and a set of known genetic markers (ITS, TEF1, CAL and FUM1). This distinguished up to 10 genetic groups, 2 clusters and 23 haplotypes among the F. proliferatum isolates. FG1056 marker showed the highest number of SNPs (169), informative sites (89) and haplotypes (23) relative to other markers used and was comparable to the multi locus typing. Varying patterns of relationships were observed between isolates represented in the genetic groups and their host and geographic origin. Considerable biological variability was recorded among the F. proliferatum isolates in morphology, growth, sporulation and most notably fumonisin production (up to 140-fold differences) with reference to variable temperature, water activity and duration. De novo genome assemblies with the size ranging from 43.96 - 50 Mb have been developed for four diverse F. proliferatum isolates. In silico analysis led to the identification of 12,980 genes common to all isolates and up to 134 genes potentially unique to an isolate. Using these resources, FUM gene cluster (~45.3 Kb) was identified for the first time in F. proliferatum. Order and orientation of the 16 FUM genes and the complete flanking genes (MSF1 and ZCB1 at 5’; ANK1 and GAT1 at 3’) have been determined. This study has provided new insights into the genetic and biological diversity of F. proliferatum and also developed new genetic and genomic resources, which will serve as a solid platform for further research particularly to understand the regulation of fumonisins production in the laboratory and in the field.
15
Fuchs, Thilo Martin. "Functional genomics of food-borne pathogens". [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980821266.
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16
Hultberg, Anna. "Lactobacilli expressing antibody fragments against pathogens /". Stockholm, 2006. http://diss.kib.ki.se/2006/91-7140-862-2/.
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17
Melander, Margareta. "Transgenic resistance to pathogens and pests /". Alnarp : Dept. of Crop Science, Swedish Univ. of Agricultural Sciences, 2004. http://epsilon.slu.se/a496.pdf.
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18
Meier, Christoph. "Structural genomics of two human pathogens". Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437351.
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Behrends, Volker. "Metabolic profiling of cystic fibrosis pathogens". Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.511871.
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20
Smith, Leanne May. "Investigating phagosome dynamics of microbial pathogens". Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/4937/.
Testo completoAbstract (sommario):
Many microbial pathogens are able to evade killing by phagocytes of the innate immune system. This thesis focuses on two pathogens: the fungal pathogen \(Cryptococcus\) \(neoformans\) and the bacterial pathogen \(Streptococcus\) \(agalactiae\). \(C\). \(neoformans\) causes severe cryptococcal meningitis in mostly immunocompromised hosts, such as those with HIV infection. In contrast, \(S\). \(agalactiae\) is the leading cause of neonatal sepsis and meningitis. The interaction between macrophages and these pathogens is likely to be critical in determining dissemination and outcome of disease in both instances. A collection of \(S\). \(agalactiae\) clinical isolates, ranging in origin from colonisation cases to severe infection cases, were tested for their ability to persist with a macrophage cell line. Surprisingly, persistence within macrophages was a characteristic shared by all of the isolates tested. Furthermore, by investigating the \(Streptococcus\)-containing phagosome, it was revealed that streptococci are able to manipulate the acidification of macrophage phagosomes. Similarly, the maturation of phagosomes containing the fungal pathogen \(C\). \(neoformans\) was explored. Cryptococci are shown to be able to manipulate the phagosome they reside within. This is driven by modified acquisition of Rab GTPases to the phagosome, as well as altered acidification and cathepsin activity within \(Cryptococcus\)-containing phagosomes.
21
Al-Groosh, D. H. A. "Opportunistic pathogens associated with orthodontic retainers". Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1419096/.
Testo completoAbstract (sommario):
Orthodontic retainers may be considered as removable implants and confer the same problems as other implants with regard to colonisation by microorganisms. Thus, biofilms forming on their surface may compromise the oral health of patients and jeopardise the efficiency of the therapy. The first part of the project involved a clinical study, a cross-sectional observational cohort, to assess the effect of orthodontic treatment on the oral microbiota and the carriage state of opportunistic pathogens during the course of treatment. High proportions of health-associated species were detected in the retainer group. However, Staphylococcus and Candida species were frequently (69% and 36% respectively) isolated from the retainers and the oral cavity of retainer wearers, where Staphylococcus spp. comprised up to 5% of the microbiota. The increase in Staphylococcus spp. including Methicillin Resistant Staphylococcus aureus (MRSA) on retainers was associated with an increase in numbers of these species on the oral mucosa of the cheek and tongue. Orthodontic retainers could, therefore, be a reservoir for pathogens and act as a source of cross-infection. A series of in vitro investigations were subsequently carried out to evaluate the effect of the surface characteristics of retainer materials, including surface roughness, hydrophobicity and surface free energy, which may affect colonisation by opportunistic pathogens. After polishing the surface of the acrylic substrata the results revealed that Atomic Force Microscope was the most appropriate device to measure the surface roughness of the acrylic and thermoplastic materials in a consistent manner. Additionally, the acid-base interactions, especially the electron donor interaction, influenced the bacterial attachment onto the thermoplastic samples. Finally, assessment of novel antimicrobial-containing acrylic resins was carried out. Firstly, incorporation of chlorhexidine showed a prolonged antimicrobial effect against MRSA but was detrimental to the mechanical properties. Thymol was successfully incorporated in heat cured acrylic materials. It reduced the surface free energy of the modified resin with no effect on the mechanical properties and was strongly antimicrobial against C. albicans. However, it showed a lesser antimicrobial effect against MRSA. This PhD has shown the potential of orthodontic retainers as reservoirs for opportunistic pathogens and that surface characteristics are significant in the retention and potential removal of these pathogens. The use of antimicrobial acrylic materials may be of potential therapeutic benefit following further development.
22
Watkins, Eleanor Rose. "The population structure of bacterial pathogens". Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:8ab53aa1-c55f-40bc-ab4f-ec2766b37252.
Testo completoAbstract (sommario):
Populations of many bacterial pathogens are structured into discrete strains despite frequent genetic exchange. Although insights from several studies suggest that different selection pressures operate in different areas of the genome, few theoretical and conceptual frameworks of bacterial population structure examine the effects of distinct competitive processes acting on different loci in the genome, and fewer still have considered the metabolic genes despite their increasingly-recognised importance in virulence. Buckee et al. (2008) investigated the combined effects of ecological competition operating at metabolic genes and immunological competition at antigenic genes on strain diversity using a stochastic model. A key prediction was that prevalent strains should show stable, non-overlapping associations between alleles of antigenic and metabolic genes. In this work, the roles of ecological and immunological competition in structuring bacterial pathogen populations is explored further using a multidisciplinary approach of mathematical modelling and whole genome analysis, focusing in particular on the well-characterised pathogens Neisseria meningitidis and Streptococcus pneumoniae as detailed case studies. We find support for the hypothesis that ecological and immunological competition play roles in structuring pathogen populations - even if present at relatively low levels - including support at the whole genome level. After extending the mathematical framework to encompass virulence-associated genes, we explore the effects of strain-targeted vaccination. We find that metabolic and virulence-associated genes from vaccine-strains are observed following vaccination in association with non-vaccine strains. The final chapter demonstrates how multilocus mathematical models coupled with whole genome analysis can be used together to gain additional insight into the evolution and population structure of bacterial pathogens.
23
Goller, Katja Verena. "Pathogens in free-ranging African carnivores". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16393.
Testo completoAbstract (sommario):
Die ökologische Rolle der meisten Wildtier-Pathogene in Bezug zur langfristigen Populationsdynamik ihrer Wirte ist nur ansatzweise erforscht und wird deshalb nur unzureichend verstanden. Stattdessen ist die Erforschung von Infektionen mit Pathogenen oft beschränkt auf einzelne Fallstudien oder auf Perioden mit deutlich erhöhten Mortalitätsraten innerhalb der Wirtspopulation. Pathogene mit geringer Virulenz können jedoch durch synergistisches Auftreten verheerende Auswirkungen auf die Fitness ihrer Wirte haben oder sich auf wichtige individuelle lebensgeschichtliche Merkmale, wie zum Beispiel Lebensdauer oder Reproduktionserfolg, auswirken. Des Weiteren sind die Auswirkungen von Krankheitserregern auf die Populationsdynamik der Wildtiere schwer abzuschätzen, zum Beispiel wenn sie die Überlebenschancen von selten zu beobachtenden Jungtieren beeinträchtigen. Bis heute sind Untersuchungen von Infektionen mit Pathogenen und deren Auswirkungen auf Lebensgeschichten meist auf Laborstudien beschränkt, in denen Tiere unter streng definierten Bedingungen gezüchtet und gehalten werden, bzw. auf Studien an kleinen, kurzlebigen Arten wie Nagern, Vögeln und Insekten oder auf Studien an der Humanpopulation. Ziel dieser Arbeit war, die Auswirkungen von Einzel- oder Koinfektionen auf individuelle lebensgeschichtliche Schlüsselparameter sowie die Einflüsse bestimmter lebensgeschichtlicher Merkmale auf den Infektionsstatus anhand einer frei lebenden sozialen Karnivorenart, der Tüpfelhyäne Crocuta crocuta, zu untersuchen. Diese Arbeit war in eine Langzeitstudie integriert und wurde an mehreren Gruppen von Tüpfelhyänen zweier Subpopulationen durchgeführt, die im Serengeti Nationalpark sowie in dem angrenzenden Ngorongoro Krater in Tansania in Ostafrika lebten. Daten über wichtige lebensgeschichtliche Merkmale von mehreren hundert individuell bekannten Tieren in Kombination mit Daten über die wechselhafte Beuteverfügbarkeit in den Territorien der Gruppen standen hierfür zur Verfügung. Ich etablierte molekularbiologische Methoden (Polymerase Kettenreaktionen (PCRs) und Reverse Transkriptions PCRs), um eine Vielzahl an Kot-, Blut- und Gewebeproben individueller Tüpfelhyänen und sympatrisch lebender Karnivoren auf das Vorkommen von Coronaviren, Caliciviren, Hundestaupe-Viren, Parvoviren sowie eines von Zecken übertragenen Blutparasiten, Hepatozoon sp., zu untersuchen. 1The ecological role of most wildlife pathogens is poorly understood because pathogens are rarely studied in relation to the long-term population dynamics of wildlife hosts. Instead, pathogen infections are reported on a case basis or studies are focused on periods when pathogens cause noticeable mortality in their hosts. However, pathogens that appear to be of low virulence may also have an important effect if they operate in a synergistic fashion or affect life history parameters such as longevity or reproductive success. Furthermore, the effect of pathogens on population dynamics may be difficult to detect in wildlife, for example if they reduce the survival of young age classes that are rarely observed. Until now, research on the life history consequences of pathogen infection has mainly been confined to laboratory studies where animals are raised and kept under strictly defined conditions, or to small, short lived species such as rodents, birds or insects, as well as to human populations. The aim of this thesis was to address these problems by assessing the impact of single infections and co-infections by pathogens on key life history parameters and the influence of life history traits on infection status in a free-ranging social carnivore species, the spotted hyena Crocuta crocuta. The study was embedded in a long-term study on several clans of spotted hyenas from two subpopulations inhabiting the Serengeti National Park and the adjacent Ngorongoro Crater in Tanzania, East Africa. Data on key life history parameters were available for several hundred individually known animals as was information on changing levels of prey availability. I established molecular biological methods (polymerase chain reactions (PCRs) and reverse transcription PCRs) to screen an extensive set of faecal, blood and tissue samples from individually known spotted hyenas and sympatric carnivores for the presence of coronavirus, calicivirus, canine distemper virus, canine parvovirus and the tick-borne blood parasite Hepatozoon sp. to determine the prevalence of the pathogens. 1
24
Abnave, Prasad. "Exploring mammalian immunity against intracellular bacteria through planarian flatworms". Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM5049.
Testo completoAbstract (sommario):
Les interactions hôte-pathogène sont un jeu vaste et complexe entre agent pathogène et hôtepour la victoire de la bataille de la pathogenèse. Plusieurs organismes modèles sont étudiéspour illustrer les mécanismes impliqués dans ces interactions. Dans ma thèse, j'ai utilisé lesplanaires comme un organisme modèle pour explorer les interactions hôte-pathogène. Comme les différents organismes modèles peuvent mettre enévidence les différentes caractéristiques de l'immunité, j'ai décidé de tirer avantage del'absence de connaissances sur l'immunité des planaires en explorant l'inexplorée. Dans monprojet, j'ai infecté les planaires avec 16 bactéries pathogènes : les planaires y sont très résistantes. Pour en explorer lemécanisme j'ai effectué un profilage du transcriptome à partir deplanaires infectées, suivie par un criblage par ARN interférence des gènes up-régulés. J'aidécouvert les gènes qui régissent la résistance antibactérienne dans les planaires, et de façonintéressante, le criblage a permis de mettre en évidence un gène, MORN2, dont la fonctionimmunologique était complètement inconnue. L'induction et l'extinction de l'expression de MORN2dans les macrophages ont révélé que MORN2 contrôle l'internalisation, la réplication et letrafic des bactéries à l'intérieur de la cellule. Dans mon étude, j'ai démontré que MORN2 estun composant de la phagocytose associée à LC3 et qu'il peut surmonter le blocage de lafusion phagolysosomale imposée par les bactéries pathogènes. Ainsi ma thèse met en avantl'importance d'utiliser des organismes modèles inhabituels afin de dévoiler des mécanismesinexplorées et des molécules impliquées dans les interactions hôte-pathogèneHost-pathogen interaction is a vast and complex interplay between pathogen and hostto conquer the battle of pathogenesis. Several model organisms are being studied to illustratethe mechanisms involved in these interactions. In my thesis I have used planarians as a modelorganism to explore host-pathogen interactions. As different model organismscan highlight different features of immunity I decided to take advantage of lack of knowledgeabout planarian immunity and get benefits from exploring unexplored. In my project I haveinfected planarians with 16 pathogenic bacteria and I found that in contrary to othercommonly used model organisms such as Drosophila, C. elegans and zebrafish the planariansare highly resistant to bacterial infections. To explore the mechanism behind this resistance Iperformed infection induced transcriptome profiling followed by RNA interference screeningof up-regulated gens. I discovered genes governing antibacterial resistance in planarians andinterestingly the screening highlighted a gene MORN2 of which the immunological functionwas completely unknown. The human ortholog of MORN2 is then further assessed for itsantimicrobial function. Induced expression and down regulation of MORN2 in macrophagesrevealed that MORN2 controls uptake, replication and trafficking of bacteria inside the cell.In my study I demonstrated that MORN2 is a component of LC3-associated phagocytosis andit can overcome phagosome maturation blockage imposed by pathogenic bacteria. Thus mythesis propounds the importance of using unusual model organisms to unveil unexploredmechanisms and molecules involved in host-pathogen interactions
25
Younis, Hussein Mariam. "Sources of human pathogens in urban waters". Thesis, Halmstad University, School of Business and Engineering (SET), 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-2354.
Testo completoAbstract (sommario):
The presence of human pathogens in water indicates the sanitary risk associated with different types of water utilization. This study surveyed the sources of human pathogens in urban waters. In order to evaluate the microbiological water quality of urban water, the enumeration of various indicator bacteria (total coliform, fecal coliform, E.coli and enterococci) is usually used.
The abundance of indicator bacteria in urban water indicates the level of fecal contamination and the presence of other human pathogens such as protozoan pathogens (Giardia lamblia & Cryptosporidium parvum).
Fecal pollution of urban waters can be from human and animal origin. Point sources of fecal contamination in an urbanized area are the effluents of urban wastewater treatment plants. While non-point sources are usually originated from diffuse sources such as (runoff from roads, parking lots, pets, leaks, failing septic systems and illegal sewer connections to storm drains). urban stormwater is considered as a major carrier for delivering human pathogens from diffuse sources to receiving waters. Increases in urban stormwater volumes have resulted from increasing urbanization and growth of impervious surfaces.
In order to reduce high amounts of human pathogens in urban waters, different methods are used nowadays to develop urban wastewater treatment plants technologies and urban stormwater management practices.
26
Hao, Xingkai. "Detection of Foodborne Pathogens Using Microfluidic Channels". Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32171.
Testo completoAbstract (sommario):
Rapid detection of foodborne pathogen is one of the most urgent problems in the world, because foodborne pathogen could cause serious illness, such as nausea, vomiting and diarrhea. We have developed a sensitive microfluidic system based on dendrimers and aptamers for rapid detection of Escherichia coli O157:H7 at very low cells concentration. Dendrimers, with high level of functional groups and homogeneous spherical shape, are prefect nanoscale polymers used as a template material by increasing sensitivity and specificity of analytes detection in microfluidics. In this work, we develop a sensitive microfluidic system based on dendrimers and aptamers for detecting Escherichia coli O157:H7 at very low cell concentrations. Carboxyl functionalized G7-polyamidoamine (PAMAM-COOH) dendrimers are immobilized on (3-aminopropyl)-trimethoxysilane (APTMS) pretreated microfluidic channels. The aptamers are subsequently conjugated on the immobilized dendrimes through chemicals. The sensitivity and specificity are validated by injecting fluorescein isothiocyanate (FITC) labelled Escherichia coli O157:H7 at various cells concentration into the resulting microchannels, indicating that the detectable cells concentration can be reached as low as 100 (cells/ml) and the detection time is 10 hours. To further exploit and improve the work efficiency our microfluidic device, the microfluidic channel is designed into a staggered herringbone microchannel (SHM) to create the chaotic dynamics inside the microfluidic device, and the SHM is then simulated by a COMSOL software showing that the staggered herringbone structures can improve chaotic dynamics of designed microchannel and will enhance the probability of particles to attach on the surface of microdevice. All the results show that our approach has the potential to develop the field of rapid and accurate detection on foodborne pathogens.
27
Chen, Desheng, e chen desheng@deakin edu au. "Development of monoclonal antibodies against Vibrio pathogens". Deakin University. Department of Biological Science, 1991. http://tux.lib.deakin.edu.au./adt-VDU/public/adt-VDU20080626.140825.
Testo completoAbstract (sommario):
Monoclonal antibodies were developed against pathogenic vibrios for use in rapid identification in disease situations of humans, fish and shellfish. Of the 12 fusions performed using V. alginolyticus, V. anguillarum, V. carchariae, V. cholerae, V. damsela, V. furnissii, V. harveyi, V. ordalii, V. parahaemolyticus and V. vulnificus, a total of 102 hybridomas were obtained. Based on cross-reactivity of a wide range of Vibrio strains and other gram-negative bacteria, three broad types of monoclonal antibodies were found. The three categories were: (1) ones that were species-specific or specific to a particular surface antigen, (2) a large number that reacted with several Vibrio species, and (3) three that reacted with most Vibrio strains but no other gram-negative bacteria.
Each species-specific monoclonal antibody only recognized its corresponding Vibrio species and was used for identifying unknown species, confirming diagnosis of clinical isolates. In addition, several monoclonal antibodies only cross-reacted with similar Vibrio species, e.g. V. parahaemolyticus and V. alginolyticus which share a common H-antigen. Monoclonal antibodies reacting with several Vibrio species were not of particular use in diagnostic situations. Three monoclonal antibodies of the last group did not react with other genera of the family Vibrionaceae, namely Aeromonas, Photobacterium and Plesiomonas nor a wide range of gram-negative enteric bacteria. These data indicated the existence of an antigenic surface determinant common to Vibrio species. One monoclonal reacted with the heat-stable antigenic determinants on the cell surface as v as lipopolysaccharide extracted from all the vibrios studied, thus making it useful for large- scale screening of acute infections of vibrios.
In a blind test, seven Vibrio species, isolated from 6 marine and a freshwater source were identified by two laboratories using phenetic tests. Results of immunotyping using monoclonals, three of seven were diagnosed as the same species, another three were designated as Vibrio species but could not be classified further due to the library not having the corresponding monoclonal, and one was diagnostically questionable. Two further tests were carried out. An unknown Vibrio formalin-fixed isolated from diseased marine animal was identified as
V. parahaemolyticus by ELISA and FITC. Clinical human isolates of V. alginolyticus, V. parahaemolyticus and V. vulnificus were confirmed by monoclonals.
Australian isolates of V. anguillarum appeared to be mostly of serotype O1. monoclonals raised to V. anguillarum AFHRL 1 reacted with only serotype O1 from Denmark but also most Australian isolates.
All vibrios pathogenic to fish and shellfish, i.e. V. anguillarum, V. ordalii, V. alginolyticus, V. carchariae, V. cholerae, V. damsela, V. harveyi, V. parahaemolyticus and V. vulnificus, were used for attachment studies to fish cells using phase contrast and FITC-immunofluorescence microscopy. Of these vibrios, V. anguillarum, V. ordalii and V. perahaemolyticus, were found to adhere to different cells and tissues of rainbow trout while others did not appear to attach. However, attachment was inhibited by monoclonal antibodies specific to only these three vibrios.
Lipopolysaccharide is well known as being a contributing factor in pathogenicity of gram-negative bacteria. PAGE electrophoresis of extracted LPS from 9 strains covering 6 Vibrio species showed the presence of a common 15,000 D fragment. This fragment was verified by immunoblotting with a genus-specific monoclonal antibody (i.e. F11P411F) recognizing nearly all vibrios. The common LPS fragment was separated and used to raise polyclonal antisera in mouse which reacted strongly with LPS itself, live as well as sodium azide-killed vibrios, but not with other gram-negative bacteria. This raised the possibility of developing vaccine from Vibrio LPS.
Monoclonal antibodies developed in the present study enabled rapid identification of a number of pathogenic Vibrio species. There is still further work to produce monoclonal antibodies against additional vibrios that are probably pathogenic. These included V. fluvialis, V. hollisae, V. metschnikovii, V. minicus, V. salmonella and V. tubiashii. Together the application will be of significance in clinical diagnostic work, in the monitoring of vibriosis in fish farms and in quarantine.
28
Williams, Katrina Anne. "Modeling post-harvest pathogens in apple fruit". Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/43746.
Testo completoAbstract (sommario):
Post-harvest disease of apple fruit causes significant loss of fruit during and after storage with a considerable economic impact. Studying the factors that contribute to post-harvest disease and developing predictive models may help growers and packing house workers to make more informed decisions on disease forecasting and duration of storage for apples. Data for three major post-harvest pathogens, Penicillium expansum, Botrytis cinerea and Mucor piriformis, which were monitored and quantified in four orchards over three years during the growing season and then in storage, were available. Contrary to expectation, it was found that environmental data provided little to no explanation of the trends in inoculum detection. It was hypothesized that this lack of relationship between the amount of inoculum present and the environmental factors was due to the manner in which the data were collected. In contrast, it was found that a large proportion of the variation in storage disease outcomes (R2=0.506, p=0.000) could be predicted by the duration of storage, temperature and rainfall two weeks before storage, and the quantity of pathogen DNA detected on the plant tissue at harvest. In order to better understand the relationship between environmental factors and spore detection in the orchard, a Gaussian plume model was developed for describing spore dispersal. Model results had good qualitative agreement with the data that were collected in the field, suggesting that a high level of variability would be expected when only using one receptor location due to the dynamics of spore movement based on wind conditions. The model predicted that increasing the number of receptors, especially when they were evenly placed around the orchard, would decrease the variability of detection results. Based on the model outcomes, it was concluded that five receptors would give the most reasonable results for the least expenditure. This research develops the first predictive model for post-harvest apple disease outcomes in storage based on pre-storage factors, and gives new insight into the dispersal of fungal spores in an orchard setting, providing recommendations for improving future data collection and modeling work.
29
O'Brien, John Kieran. "Interactions between bovine leucocytes and respiratory pathogens". Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254519.
Testo completo
30
Scholes, Julie Diane. "The effects of biotrophic pathogens of photosynthesis". Thesis, Bangor University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.237087.
Testo completo
31
Tallentire, Eva Elizabeth. "Novel methods of controlling targeted potato pathogens". Thesis, University of Newcastle Upon Tyne, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519481.
Testo completo
32
Woo, Chiu-yat Patrick, e 胡釗逸. "Defining novel clinical syndromes and emerging pathogens". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B27497343.
Testo completo
33
Lin, Xiaonan. "Chemical and Cellular Defenses against Foreign Pathogens". Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10354.
Testo completoAbstract (sommario):
Bacterial and viral infections affect billions of people each year. While bacterial infections are treated by the use of antibiotics, viral infections are eradicated by the immune system. This thesis comprises two parts. Part I presents the reconstitution of enzymes required for the synthesis of the minimal pharmacophore of moenomycin A (MmA), a molecule with antibacterial activity. Part II details single-particle electron microscopy studies of MDA5 alone and in complex with double-stranded RNA (dsRNA). MmA is a natural product antibiotic from Streptomyces ghanaensis that possesses remarkable potency against clinically relevant Gram-positive bacteria. MmA exerts its antibacterial activity by binding directly to peptidoglycan glycosyltransferases, enzymes involved in the synthesis of the glycan strands of peptidoglycan. The genes responsible for MmA biosynthesis have been identified, and a complete biosynthetic pathway has been proposed. Part I of this thesis describes the reconstitution of enzymes required for the synthesis of two trisaccharide scaffolds of MmA that retain antibacterial activity. It also describes the synthesis of unnatural phosphoglycerate lipid acceptors and UDP-amino sugars that can be used to probe the substrate tolerances of key glycosyltransferases in MmA biosynthesis. This work lays the foundation for the synthesis of unnatural MmA analogs that may possess better pharmacokinetic properties than the parent molecule. MDA5 is a helicase that detects viral dsRNA in the cytoplasm of vertebrate cells. Upon dsRNA recognition, MDA5 initiates a series of signal transduction events that activate the innate immune response. Part II of this thesis presents the structures of apo MDA5 protein and the MDA5-dsRNA complex obtained by using single-particle electron microscopy. Two-dimensional averages of apo MDA5 revealed that the protein is very flexible and can adopt multiple conformations. This finding suggests that MDA5 does not adopt an autorepressed conformation in the absence of viral dsRNA. When MDA5 is incubated with dsRNA, the protein assembles onto the dsRNA to form a linear oligomer. Two-dimensional averages and a three-dimensional reconstruction reveal the complex to consist of seven to eight stacked discs per strand of 112 base pair dsRNA. This work lays the foundation for further structural studies aimed at elucidating the mechanism by which MDA5 is activated.Chemistry and Chemical Biology
34
Sutherland, Margery Louise. "Recognition of host plants by vascular pathogens". Thesis, University of Reading, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303155.
Testo completo
35
Knell, Robert James. "The population ecology of two insect pathogens". Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284218.
Testo completo
36
Frey, Andrew. "Investigation of the sialidases of periodontal pathogens". Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/16411/.
Testo completoAbstract (sommario):
Periodontitis results in destruction of tooth supporting structures, eventually leading to tooth loss, and it affects ~10% of the world's population. Key to its onset and progression is a complex relationship between the periodontal bacteria and the host inflammatory response. The bacteria most associated with severe periodontitis are the so-called periodontal pathogens of the red complex- Tannerella forsythia, Treponema denticola, and Porphyromonas gingivalis. These organisms all express sialidases, which cleave sialic acid from host glycoproteins, and this is believed to contribute to disease. Considering this, the aims of this project were to further characterise the sialidases of T. forsythia and P. gingivalis (NanH and SiaPG), to test their inhibition with commercially available chemotherapeutics, and the effect this has on in vitro models of virulence. NanH and SiaPG were successfully purified by affinity chromatography. The enzymes were shown to possess a high degree of activity over various conditions and on different sialic acid ligands. Importantly, both sialidases could be inhibited using the commercially available chemotherapeutic zanamivir (supplied by GlaxoSmithKline, UK) which laid the groundwork for studies testing inhibition of virulence. The accessory enzyme NanS was shown to bolster sialic acid release from bovine salivary mucin by both NanH and SiaPG. This was important for nutrient acquisition, since NanS also enhanced the growth of P. gingivalis in defined media where serum and saliva were the only nutrient sources. These findings also hinted at the possibility of interspecies cooperation in sialic acid release from host sources. Zanamivir also inhibited biofilm formation of P. gingivalis on oral-relevant glycoprotein sources. Zanamivir was also shown to be capable of inhibiting attachment and invasion of oral epithelial cells by P. gingivalis, T. forsythia, and the sialidase negative pathogen Fusobacterium nucleatum, even when multiple species were present during infection. Finally NanH was shown to part-mediate pro-inflammatory signalling in oral epithelial cells in response to P. gingivalis LPS, and zanamivir prevented pro-inflammatory cytokine release in cells infected with T. forsythia. This highlighted multiple mechanisms by which sialidase inhibition can prevent host-pathogen interactions. This study broadens our understanding of the multifarious roles of bacterial sialidases in virulence, and indicates that their inhibition with chemotherapeutics could be a promising strategy for periodontitis therapy.
37
Patrick, Sheila. "Opportunistic pathogens of the normal human microbiota". Thesis, University of Edinburgh, 2006. http://hdl.handle.net/1842/25062.
Testo completoAbstract (sommario):
To the colonising bacterium, the human body represents a number of ecological niches, some of which it could be argued are as hostile to the coloniser as even the most extreme of ex vivo environments; by the activities of the immune system, these living host niches are actively dedicated to the prevention of their colonisation. Paradoxically, the normal human microbiota of each human extends in estimated total number to approximately 1014 per human. This thesis is a compilation of published work that focuses on two anaerobic bacteria of the normal human microbiota: Bacteroides fragilis predominantly found in the large intestine; and Propionibacterium acnes predominantly found in the skin microbiota. When given the opportunity these bacteria can cross the divide between commensal and pathogen and cause infection. The papers included in this thesis address aspects of the characteristics of these bacteria that may relate to virulence and the association of these bacteria with clinical infection.
38
Vágány, Viktória. "Characterisation of fusarium pathogens in the UK". Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/56393/.
Testo completoAbstract (sommario):
The primary aim of this project was to identify and characterise Fusarium species associated with the basal rot of Allium species and internal fruit rot of sweet peppers in the UK. The secondary objective was to develop quick molecular markers to identify Fusarium oxysporum f. sp. cepae (FOC) causing onion basal rot. Isolates representing diverse Fusarium species taken from onions, garlic, shallot and leeks obtained from different production and processing sites in the UK were collected. F. proliferatum was found for the first time to be a causal agent of onion basal rot in the UK, but F. oxysporum was by far the most common species and F. oxysporum isolates belonged to at least two different genotypes based on a sequence comparison of several “housekeeping” genes, and overall, appeared to be polyphyletic. None of the housekeeping genes studied correlate with pathogenicity. Secreted in xylem (SIX) genes offer more promise for the specific identification of F. oxysporum formae speciales (Lievens et al., 2009a) and a homologue of the SIX7 gene was found only in a few FOC isolates suggesting that SIX7 is not absolutely necessary for pathogenicity. Whole genome sequencing of a FOC isolate was carried out in order to understand pathogenicity and identify novel effector genes. This work revealed the presence of further homologues of published SIX genes, namely SIX3, SIX5 and SIX9. The presence of SIX3 and SIX5 has only been reported from F. oxysporum f. sp. lycopersici previously. Additionally, screening of eleven new candidate effector genes suggested that FOC isolates have different gene sets which correspond to the continuous variation of aggressiveness found within the FOC population. Fusarium lactis, F. proliferatum and F. solani were identified in association with internal fruit rot of sweet pepper obtained from three different production sites in the UK.
39
Poole, Sophie. "Aetiological links between oral pathogens and dementia". Thesis, University of Central Lancashire, 2014. http://clok.uclan.ac.uk/11156/.
Testo completoAbstract (sommario):
Introduction: Several observational studies support an association between periodontal disease and Alzheimer’s disease (AD). Poorly managed oral hygiene together with the immunosuppressed status of demented patients appears central to this hypothesis as together they contribute not only to an increased incidence of oral infections but also to recurrent bacteraemia that can seed oral bacteria into systemic circulation. The aim of this study was to establish a link between periodontal disease and AD with a view to identifying the red complex periodontal disease bacteria (Treponema denticola, Tannerella forsythia and Porphyromonas gingivalis) and/or bacterial components in human AD and non-AD brain tissue and explore the proof of concept of the red complex bacteria accessing the brain of ApoEnull mice during experimental periodontitis, and assess how they may contribute to the development of AD pathology. Methods: Molecular techniques (PCR, cloning and sequencing) were employed for investigating the presence of bacterial DNA within the specimens (human or mouse) using two different approaches (universal and species specific primers). The presence of specific virulence factors were determined using anti-bacterial antibodies. The innate immune responses were detected using antibodies against complement activation, alongside inflammatory assessment using specific antibodies for activated microglia and astrocytes. Further, histology staining was used to assess tissue preservation and the presence of pathological hallmarks of AD. Results: Human AD and non-AD controls failed to demonstrate the presence of red complex pathogens when analysed using molecular methodologies. However, immunofluorescence labelling of a virulence factor (LPS) was positive for P. gingivalis in 4 out of 10 AD cases. Immunoblotting demonstrated bands corresponding to P. ginigivalis LPS in the same AD brain specimens (p = 0.029). Analysis of brain tissue from ApoEnull mice induced with periodontal disease using molecular methods demonstrated 6 out of 12 ApoEnull mice brains contained P. gingivalis genomic DNA at 12 weeks (P = 0.006), and increased to 9 out of 12 at 24 weeks (P = 0.0001). In addition, tissue sections of infected mice demonstrated periodic acid-Schiff (PAS)-positive, argyrophilic inclusions in the hippocampus at both time points, which also labelled positive with the bacterial-specific anti-peptidoglycan antibody. Also, it was noted that microglia in both infected and control groups demonstrated strong intracellular labelling with C3 and C9, presumed on-going biosynthesis, however, the pyramidal neurons of the hippocampus in 4 out of 12 P. gingivalis infected mice brains were clearly opsonised with C3 activation fragments (P = 0.032) suggesting they were under attack from complement mediated lysis. Conclusion: These results show P. gingivalis was able to access the brain of humans and ApoEnull mice, supporting the concept of the focal infection theory. Together these results suggest a potential link with AD via the periodontal pathogen translocating from its original oral niche to the brain. ApoEnull mice induced with periodontal disease demonstrated the intracerebaral innate immune responses were initiated by local CNS cells, which not only contributed to a higher inflammatory burden but also bystander damage of functional neurons in the hippocampus area of the brain which is associated with memory. Although further research is needed to establish clinical measures that demonstrate a cause and effect relationship between oral infections and AD, this study does provide initial support to the role of periodontal pathogens in the development of dementia. Early treatment of periodontal disease in addition to greater awareness of the importance of maintaining good oral health may halt or slow down the progression of this debilitating disease.
40
Dearlove, Bethany Lorna. "Genome evolution and epidemiology of human pathogens". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:af385d35-ca1a-4f4c-ae1a-0ad954cab928.
Testo completoAbstract (sommario):
Understanding the transmission dynamics of infectious diseases is important to well-informed public health policy, responsive infection control and individual patient management. The on-going revolution in whole-genome sequencing provides unprecedented resolution for detecting evidence of recent transmission and characterising population-level transmission dynamics. In this thesis, I develop and apply evolutionary approaches to investigating transmission, focusing on three globally important pathogens. Hepatitis C virus (HCV) is a major cause of liver disease affecting 150 million people and killing 350,000 annually. I conducted a meta-analysis of twentieth-century HCV epidemics, finding that the age of the epidemic can be predicted by genetic diversity. Using the coalescent, I fitted classic susceptible-infected (SI), susceptible-infected-susceptible (SIS) and susceptible-infected-recovered (SIR) epidemiological models. Most epidemics showed signatures of SI dynamics, but three, from Argentina, Hong Kong and Thailand, revealed complex SIR dynamics. Norovirus is the leading viral cause of diarrhoea, estimated to cost the NHS around £115 million annually. I analysed whole norovirus genomes via a stochastic transmission model, finding that up to 86% of hospital infection was attributable to transmission from another patient in the hospital. In contrast, the rate of new introductions to hospital by infected patients was extremely low (<0.0001%), underlining the importance of ward management during outbreaks. Campylobacter is the most commonly identified cause of bacterial gastroenteritis worldwide. I developed a zoonotic transmission model based on phylogeography approaches to test whether three strains previously associated with multiple host species were in fact aggregates of strongly host-restricted sub-strains, or genuine generalists. Members of the same strain isolated from different host species were often more closely related than those isolated from the same host species. I estimated 419, 389 and 31 zoonotic transmissions in ST-21, ST-45 and ST-828 respectively, strongly supporting the hypothesis that these strains are adapted to a generalist lifestyle.
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Smith, Sara Jean. "Attachment and Biofilm Formation of Foodborne Pathogens". Thesis, North Dakota State University, 2017. https://hdl.handle.net/10365/28387.
Testo completoAbstract (sommario):
Outbreaks of Listeria monocytogenes, Salmonella, and Escherichia coli are increasingly attributed to fresh produce. Current control measures have been assessed for decades, with no alternatives adopted. Sources were identified, reducing flhD transcription and biofilm amounts nearly 2-fold. ?-phenylethylamine (PEA), reduced growth and biofilm 96% and 70%, respectively. Curli production was assessed and found to be microorganism-, strain-, and/or serotype-dependent. Reporter fusions were constructed, evaluating expression of Listeria cellulose protein (Lcp). Plcp was not impacted by conditions used. Conditions were then used in attachment of L. monocytogenes to stainless steel. Attachment was significantly reduced by 5 ppm chlorine and 2% lysate. Small molecules could be alternatives to current control measures. More research is needed on what induces curli production. Controls confirm that reporter fusions are an effective way to discover signals impacting gene expression. Attachment/expression assays, indicate that something other than Lcp are responsible for changes in attachment to stainless steel.
42
Mastropaolo, Matthew David. "Studies of Three Human Intestinal Opportunistic Pathogens". Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28529.
Testo completoAbstract (sommario):
Opportunistic bacterial pathogens are present in the intestines of all mammals. These bacteria are symbionts to a certain extent, but under certain conditions these organisms can be deadly. Intestinal opportunistic pathogens encompass many genera and include organisms such as those in the Bacteroides fragilis group (i.e. B. fragilis and B. thetaiotaomicron), Escherichia coli, and Clostridium perfringens, resulting in an array of diseases and serious health risks. Typically these diseases affect individuals in poor or weakened health (elderly, immuno-compromised, neonates, etc.) but can affect healthy individuals as well. The intestinal tract is the main area of infection for these bacteria, however some of these organisms can be involved in wound infections, septicemia, urinary tract infections, and meningitis. This study focused on three areas: 1) Analysis of differences in gene expression between Bacteroides and Escherichia coli, in order to learn more about promoter structure, 2) Establishment of a diabetic mouse model for use in examining bacterial synergy during a polymicrobial infection, and 3) Characterization of Escherichia coli 360A and evaluation of the role of several virulence factors and environmental modulators in the pathogenesis of this strain.
We used a newly developed lux gene reporter to evaluate gene expression in Bacteroides. We observed that there are barriers in both transcription and translation initiation that appear to limit the expression of foreign genes in Bacteroides. We were able to establish a mouse model for studying synergy during a polymicrobial infection and observed that E. coli 360A provided synergy towards B. fragilis NCTC 9343. These experiments also showed that the longer a mouse is afflicted with the complications of diabetes the more susceptible it is to polymicrobial infections. Systemic infections were used to evaluate the contribution of several virulence factors and environmental modulators in the pathogenesis of E. coli 360A. The results showed that a strain lacking both virulence factors CNF1 and HlyA, the terminal oxidase cytochrome o, or a double cyo/cyd mutant were, deficient in survival in the spleen, but not the liver of BALB/c mice.Ph. D.
43
Szwetkowski, Kyle John. "Methylobacterium spp.: Emerging Opportunistic Premise Plumbing Pathogens". Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/77659.
Testo completoAbstract (sommario):
Opportunistic premise plumbing pathogens (OPPPs) are responsible for many infections linked to drinking water. The annual cost of disease caused by these waterborne pathogens is $850 million. Key characteristics of these opportunistic waterborne pathogens include: disinfectant- resistant, biofilm formation, thermal-tolerance, desiccation-resistant, growth in amoebae and growth in low oxygen conditions. Methylobacterium spp. have been recognized as an emerging OPPP, so the purpose of this study was to investigate these waterborne bacteria in more detail to determine whether they have all characteristics of OPPPs. Seven Methylobacterium spp. strains were studied to measure growth in laboratory broth medium and drinking water, measure hydrophobicity on surfaces found in household plumbing, measure adherence and biofilm formation to surfaces found in household plumbing and measure susceptibility to hot water heater temperatures. Methylobacterium spp. were found to aggregate in lab broth medium and drinking water, hydrophobic on different surfaces in household plumbing, adhere readily and form biofilm on different surfaces and thermal-tolerant to water heater temperatures. These results support and identify Methylobacterium spp. as opportunistic premise plumbing pathogens.Master of Science
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Gallegos, Karen M. "Characterization of Pathogens for Potential Diagnostic Tests". University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1367942509.
Testo completo
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Sampson, Mark M. "Role of chitinases in bacterial insect pathogens". Thesis, University of Aberdeen, 1997. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU117909.
Testo completoAbstract (sommario):
Chitinases have been proposed to play a key role in the virulence of microbial insect pathogens. The chitinolytic properties of the biopesticides Bacillus thuringiensis and Bacillus sphaericus were investigated using in vitro enzyme assays and in vivo bioassay studies. It was observed that when a suspension of 'colloidal' chitin was added to a solution of Calcofluor White M2R there was a significant enhancement of fluorescence observed. Using this observation a plate-reader chitinase assay was developed and the activities of a range of B.thuringiensis strains were measured. A similar fluorescent effect was observed with a glycol chitosan suspension and a chitosanase assay was developed. The chitosanase enzyme properties of B.thuringiensis strains were also characterised. More detailed analysis of the chitin and chitosan degrading properties of three selected strains of B. thuringiensis were performed using enzyme assays and SDS-PAGE activity gels. To investigate the role of chitinases in B.thuringiensis, bioassay studies were developed using 4th instar larvae of the biting midge C.nubeculosus and newly hatched caterpillars of the cotton leaf worm S.littoralis. Samples of B.thuringiensis were added at a range of concentrations along with additions of either an exogenous chitinase preparation or the specific chitinase inhibitor allosamidin. The results showed the addition of chitinase to enhance the insecticidal activity and addition of allosamidin to inhibit insecticidal activity of B.thuringiensis. Collectively, the data shows chitinase and chitosanase production to be widespread among different subspecies and pathotypes of B.thuringiensis and also, shows chitinases to play an important role in the virulence of B.thuringiensis.
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Giannakopoulou, Artemis. "Approaches towards disease resistance to filamentous pathogens". Thesis, University of East Anglia, 2015. https://ueaeprints.uea.ac.uk/58580/.
Testo completoAbstract (sommario):
In the co-evolutionary arms race between plants and pathogens, plants have developed a multifaceted armory consisting of diverse defence responses, such as the production of antimicrobial compounds and the activation of immunity via specific receptors. This work examines the use of the phytoalexin capsidiol and synthetic NLR immune receptors as disease resistance approaches against oomycete and fungal plant pathogens. The production of phytoalexins constitutes an important aspect of plant defence. Capsidiol, a pepper phytoalexin, differentially inhibits the growth of two Phytophthora species, the late-blight pathogen P. infestans and the vegetable pathogen P. capsici. The differential effect of capsidiol towards these two oomycetes was determined and quantified. I also monitored intraspecific variation among various P. infestans isolates in their sensitivity towards capsidiol. Plant defence machinery also involves intracellular immune receptors of the Nucleotidebinding Leucine-rich Repeat-containing protein family (NLRs). NLRs typically recognize pathogen effector proteins with avirulence activities, leading to a response known as effector-triggered immunity (ETI). R3a and I2 are orthologous NLRs from potato and tomato responding to effectors of P. infestans and the wilt fungus Fusarium oxysporum f. sp. lycopersici, respectively. Yet, particular races of these pathogens have evolved stealthy effectors that evade recognition by R3a and I2. I assessed whether previously identified mutations in R3a, with expanded response specificities to Phytophthora spp. effectors, can be transferred to I2 with similar beneficial effects. I recovered I2 mutants with expanded response spectrum to effectors from both P. infestans and F. oxysporum f. sp. lycopersici. Infection assays in both transient and stable transgenic systems suggested this expanded response correlates with resistance. I finally investigated whether the I2 locus is a determinant of tomato resistance against P. infestans. Overall, these findings generate new insights into the molecular interactions underlying plants response to pathogens, and open up applied perspectives for sustainable crop disease resistance.
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Anderson, Christopher. "Pathogens of cotton seedlings in NSW Australia". Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/12804.
Testo completoAbstract (sommario):
This study aimed to further expand understanding of the pathogens of cotton seedlings across NSW, and to identify pathogens associated with increased seedling mortality in southern NSW. A total of 230 organisms were recovered into pure culture from 192 locations and most screened for pathogenicity. The genera Rhizoctonia, Pythium, Fusarium, Macrophomina, and Sclerotium were isolated from diseased tissues and pathogens included R. solani anastomosis group (AG) 2-1, 2-2 IIIB, 3, 4 HG-I and 4 HG-III, Pythium sp., P. ultimum, P. helicoides and S. rolfsii. Pathogenicity of R. solani AG 3 and P. helicoides against cotton is novel. Pathogenic Pythium spp. were more commonly associated with samples from southern NSW. There was no variation in aggressiveness between isolates of Pythium from northern and southern regions, and pesticide controlled pathogen growth on amended agar and seedling disease in pots. The aggressiveness of Pythium spp. towards cotton was increased under temperatures reflective of Griffith NSW indicating that cool temperatures are probably the main driver behind increased aggressiveness of Pythium spp. and may account for historically high levels of seedling death in the south. Isolates of P. helicoides were insensitive to metalaxyl-M on pesticide amended agar and when exposed to pesticide seed treatment and caused root rot. Among AGs of R. solani, isolates of AG 4 HG III grew fastest among isolates at 30°C, whilst isolates of AG 4 HG I were most aggressive at all temperatures. Isolates of AG 2-1 displayed an intermediate level of aggressiveness and insensitivity to azoxystrobin. Isolates of AG 2-2 IIIB and AG 3 caused the lowest levels of disease among isolates. A distinct clade was identified among AG 3 ITS sequences belonging to isolates from cotton in Australia. AG 3 isolates from cotton caused disease on cotton seedlings but not on potato suggesting support for the phylogenetic specialisation of AG 3 on cotton or the Malvaceae in Australia.
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Gonzalez-Alanis, Pablo. "The Inactivation of Pathogens in Aquaculture Systems". Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/195899.
Testo completoAbstract (sommario):
As aquaculture has become a significant provider of the human diet, the interest to have better quality of sea and fresh products has been increasing. However the potential hazards associated with pathogenic agents resulting in losses to the industry are major concerns that provided the motivation for this study.The use of ultraviolet irradiation is an alternative to disinfect water in inlet and outlet water sources. However the ultraviolet disinfection method has some drawbacks including no disinfectant residuals and high cost of lamp fouling and replacement. The ultraviolet system needs to be calibrated according with the life time of the ultraviolet lamps.The MS-2 coliphage in this study is an approach to determine a good indicator for determining if an ultraviolet system can be effective in an aquaculture recirculation system. The susceptibility of this system can provide an indication if WSSV can be inactivated and possible other pathogenic agents.The WSSV experiment was successful in reducing mortality. Further studies have to be completed and analyzed before recommending for control of other pathogens.
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Gherghisan-Filip, Cristina. "Engineering novel lantibiotics to target gut pathogens". Thesis, University of East Anglia, 2016. https://ueaeprints.uea.ac.uk/63830/.
Testo completoAbstract (sommario):
Infections with multi-drug resistant bacteria are an urgent health security threat and bacteriocins such as the subclass of lantibiotics represent a promising alternative source to traditional antibiotics. The gut intestinal tract ecosystem has a complex set of bacteria with a huge bacteriogenic potential and it can be explored as a source for new lantibiotic peptides. Using a genome mining approach, a clos gene cluster that has the potential to encode for novel lantibiotics was previously discovered in a strain of Blautia isolated from the human gut. This clos operon may encode two nisin-like peptides. Several nisin derived clos-like sequences were generated, however they did not have improved properties when tested under GI tract conditions. Since we lack the molecular tools to manipulate the original Blautia obeum A2-162 gut bacterium that harbours the clos operon, the entire clos cluster was cloned in Lactococcus lactis where it was possible to obtain heterologous expression of the Clos peptides under the control of the nisin inducible NisRK regulatory system. The production of preClosA was demonstrated using an antibody raised against the Clos leader. The biological activity of the Clos peptide was confirmed after treatment with trypsin where the Clos leader was presumably cleaved, releasing the biologically active and mature Clos peptide that was highly active against two clinically important pathogens, Clostridium perfringens and Clostridium difficile as well as against L. lactis MG1614 sensitive indicator strains. Using immunoprecipitation, we obtained pure Clos peptides in solution and after trypsin treatment and alkylation of the cysteine residues, the post-translational modifications and the structure of the preClosA peptides were confirmed. Some of the anticipated dehydrations and ring formations (Rings D and E) were also identified using LC-MS. The approach taken in this PhD project confirms that genome mining can be used to identify more gut bacteria with potential to produce novel lantibiotics.
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Volpe, Enrico <1987>. "Finfish and Human Pathogens in Bivalve Molluscs". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amsdottorato.unibo.it/8062/1/Tesi%20PhD_Volpe%20Enrico.pdf.
Testo completoAbstract (sommario):
Bivalve molluscs are an important food source for living beings, humans included. They are obligated filter feeders, that feed on microalgae, bacteria and organic particles present in the aquatic environment. Accordingly, they could accumulate chemical compounds, marine biotoxins, bacteria and viruses, including human and animal pathogens (Molloy et al., 2013; Serratore et al., 2014), influencing the epidemiology of animal and human infectious diseases (Skär & Mortensen, 2007).
This topic has been long investigated for human pathogens. On the other hand, poor studies were available for finfish pathogens.
The Ph.D thesis, arranged in three chapters, deals with finfish and human pathogens in bivalve molluscs and focus on betanodavirus presence in these invertebrates, on their interaction with the Redspotted grouper nervous necrosis virus (RGNNV), one species of the genus Betanodavirus, and the development of a method to mitigate bacterial and viral contaminations of bivalve molluscs.
Betanodaviruses very closely related to those of finfish have been found widely present in bivalve molluscs. The clams were demonstrated able to take up and then shed viable RGNNV into the surrounding environment through faeces and filtered water into the surrounding environment posing a serious risk for susceptible cohabitant fish species. Finally, a novel Manila clam sea water potassium MPS-based disinfection method was set up to mitigate the impact of bacterial and viral contaminations in bivalve molluscs.
The obtained results point out the possible role of bivalve molluscs in the transmission of pathogens to finfish and highlight the needing of surveillance and control activities where a close inter-specific contact is present. The proposed novel disinfection method provides good experimental results and could find wide application in fisheries sector after adequate field tests.