Rozprawy doktorskie na temat „Antibacterial therapeutics”

In this thesis gallic acid-triethylene glycol (GATG) dendrimers were synthesised and efficiently functionalized with hydroxyl groups, phenylboronic acids and primary amines. The interactions of the dendrimers with bacteria and the potential for development of new antimicrobials were evaluated in this study. Specifically, the ability of the dendrimers to induce bacterial clustering and interfere with small molecule autoinducer-2 (AI-2) in the Quorum Sensing (QS) pathway of the marine bacteria V. harveyi was studied with the use of Coulter Counter aggregation assays and detection of QS–controlled luminescence. Novel alkynylated ligands with diol-, tetraol-, glucose- and mannose- moieties were synthesised and successfully functionalized to GATG dendrimers of generation G1 and G3 through catalyst-free azide-alkyne cycloaddition (AAC). The results of luminescence experiments reveled that the dendrimers functionalized with hydroxyl groups decreased AI-2 induced luminescence of V. harveyi MM32 at the at early time points (4 h) while a dose-dependent increase of luminescence and increased bacterial growth was observed at later time points. GATG dendrimers of generation G1 and G3 were decorated with 9 and 81 phenylboronic acid in the periphery. These dendrimers had an inhibitory effect on growth and luminescence as observed by luminescence, aggregation and colony forming unit-counting assays. Although the mechanism is not yet fully understood, these promising results should be further explored. Cationic GATG dendrimers of generation G1, G2 and G3 with 9, 27 and 81 primary amines in the periphery induced formation of clusters in V. harveyi in a generation dependent manner, an improved ability to induce cluster formation when compared with poly(N-[2- (dimethylamino)propyl]methacrylamide), a cationic linear polymer previously shown to cluster bacteria. Viability of the bacteria within the formed clusters and the evaluation of the QS controlled luminescence suggests that the GATG dendrimers may be activating microbial responses by maintaining a high concentration of QS signals inside the clusters while increasing permeability of the microbial outer membrane. Thus, a generation-dependent effect in bacterial luminescence production and membrane permeability was induced by the cationic dendrimers. The inhibition of growth and increased membrane permeability in combination with cell clustering may be promising antibacterial features of these dendrimers. These results highlight the potential of the GATG dendritic platform to develop new antimicrobials aimed to target microbial viability and/or virulence (e.g. adhesion) and encourage further investigations on the importance of polymeric architecture and multivalency in the antimicrobial field.

The widespread use of antibiotics has played a significant role in the emergence of resistant bacteria. It is of great interest and need to develop novel, effective and safe antimicrobial therapeutics. The biosynthesis of bacterial cell wall peptidoglycan is an intricate process that has become a popular target for antibiotics. Lytic protein E of Bacteriophage ΦX174 was found to inhibit peptidoglycan biosynthesis via an unknown interaction with integral protein MraY. Genetic studies have revealed that E-mediated lysis is dependent on the interaction between Phe288 of MraY and the transmembrane segment of protein E. We have constructed an α-helical model for the predicted transmembrane interactions between protein E and MraY and shown that favourable interactions can be formed between Phe288 and the RWXXW motif of protein E. In this thesis, analogues of the RWXXW motif were synthesised in solution and via solid phase peptide synthesis using 2-chlorotrityl chloride resin as the polymeric support. The inhibitory activity of these analogues was determined on a continuous fluorescence assay against membrane bound MraY. Inhibition studies on site-directed mutants of E. coli MraY were also conducted. Testing the inhibitory activity of RWXXW analogues provided compelling information on the importance of protein E residues for the inhibition of MraY. Peptides which contained a tryptophan residue were especially good inhibitors of MraY presumably due to their interaction with Phe288. Mutation of Phe288 caused a dramatic decrease or complete loss to the inhibitory activity of peptides containing an aromatic residue. Some analogues also contained antibacterial activity across multiple strains of bacteria including E. coli, B. subtilis and P. putida with MIC values as low as 8μg/mL. To confirm if MraY was the target enzyme, E. coli cells overexpressing MraY were treated with RWXXW analogues. An increase in the MIC of RWXXW analogues signified that the MraY was the lysis target. In the course of the project, we noticed that members of the UPA class of natural products contained some structural features that are also found in the RWXXW motif. These natural products were tested for activity against site-directed mutants of E. coli MraY. Results showed that Phe288 plays some role in the inhibition of MraY by pacidamycin. This work identifies a promising target for the development of novel antimicrobial agents that is located on the outer face of the cytoplasmic membrane.

Clostridium difficile is one of the UK’s most common hospital acquired infections and there is anecdotal evidence to suggest that the bacteria are sensitive to the antibacterial properties of tea. Surprisingly, little research has been undertaken to characterise the inhibitory activity of aqueous tea infusions that are representative of traditional drinking habits. The antibacterial properties of tea are thought to be due to a group of polyphenols called catechins. However, their contribution to the inhibitory activity of tea infusions and their mechanism of action is still subject to debate. An antimicrobial assay, developed using Staphylococcus aureus as a model organism, was used to determine the antibacterial activity of a range of tea infusions against 75 clinical isolates of C. difficile that represented all the major strain ribotypes over 11 years. Green teas demonstrated more potent antibacterial activity than black teas and their activity was positively correlated with antioxidant power, hydrogen peroxide production, and catechin content. Furthermore, the country of origin of the tea affected the catechin content and subsequent antimicrobial activity of the infusion. Detailed chemical analysis using high performance liquid chromatography and counter current chromatography suggests that the antibacterial activity of tea is probably the result of synergistic interactions between a number of catechins rather than the activity of an individual compound. With regards to the mode of action by which tea inhibits C. difficile, electron microscopy studies of the bacterium treated with green tea revealed distinct changes to the outer cell structures of the bacteria. These changes were indicative of cell membrane blebbing, thus supporting the theory that tea compounds interact with the bacterial membrane and/or cell wall. Overall, this investigation concluded that tea infusions have inhibitory activity against C. difficile in vitro and may be useful in the treatment or prevention of C. difficile infections in vivo.

Clays and clay minerals (phyllosilicates) have been used for millennia to treat a range of human maladies, such as infected wounds and diseases of the skin. The unique chemistry of phyllosilicates allows them to support the wound environment and encourage healing. Their physicochemical properties can also be utilised to develop modified drug-release formulations and also enables their incorporation into polymer matrices for the development of advanced wound care materials. By developing novel antibacterial phyllosilicate-polymer composite materials it should be possible to support wound healing, whilst simultaneously treating infections locally to avoid systemic adverse effects and prevent the development of antimicrobial resistance. In this research project the clay minerals kaolin (KN), refined montmorillonite (rMMT), montmorilonite K10 (MMTK10), Laponite® RD (LRD), and Laponite® XL21 (LXL21) were investigated for their differing structure and physicochemical properties. Their ability to adsorb and desorb the antibacterial agents tetracycline (TC), doxycycline (DC) and ciprofloxacin (CIP) was determined through a series of adsorption kinetics and isotherm studies. LRD and LXL21 were shown to have the highest drug-carrying capacity and were also able to relinquish this drug-load to inhibit the proliferation of key wound pathogens; Staphylococcus epidermidis, Propionibacterium acnes, and Pseudomonas aeruginosa. XRD and FTIR analyses demonstrated that these drug molecules could be adsorbed into the interlayer space and edge groups of the Laponite® particles. LXL21-CIP composites were successfully incorporated into alginate polymer matrices through interaction of the exposed edge-groups on LXL21 and the hydroxyl groups of the alginate to produce novel nanocomposite film and foam materials. Selection of candidate materials was initially undertaken qualitatively with the support of a tissue viability nurse at the Royal Liverpool and Broadgreen University Hospitals NHS Trust. Important properties for wound-dressings such as adsorptive capacity, water vapour transmission rate, and keratinocyte compatibility were measured quantitatively and compared to materials already used for wound care in the UK. Both the film and foam materials were shown to have properties that would be beneficial for wound healing and were also able to release CIP in a controlled manner with notable activity against S. epidermidis, P. acnes, and P. aeruginosa. The nanocomposite film formulation developed in this research project showed promise for future clinical applications and future work should be undertaken to further optimise their manufacture and fully characterise their ability to support the healing of infected wounds. Although the nanocomposite foams require further research, the work presented in this thesis suggests they could also be promising materials for wound care applications.

Protein translocation is essential for bacterial survival and the most important translocation mechanism in bacteria is the secretion (Sec) pathway. Thus targeting Sec pathway is a promising strategy for developing novel antibacterial therapeutics. We report the design, syntheses, mechanistic studies and structure-activity relationship studies using HQSAR and 3-D QSAR Topomer CoMFA analyses of 4-oxo-5-cyano thiouracil derivatives. In summary, introduction of polar group such as –N3 and linker groups such as –CH2-O- enhanced the potency as well as logP and logS several fold. We also report the discovery, optimization and structure-activity relationship study of 1,2,4-triazole containing pyrimidines as novel, highly potent antimicrobial agents. A number of inhibitors have been found to inhibit microbial growth at high nanomolar concentrations.

Cyclic dipeptides (CDPs) are amino acid-based compounds, some of which possess antibacterial activity. The encapsulation of certain drugs into liposomes has been found to improve their activity in terms of bioavailability and duration of action. Liposomes are small vesicles that are under investigation as drug carriers for the delivery of therapeutic agents. A number of liposome formulations are currently under clinical trial review, whilst some have already been approved for clinical use. The aim of this study was to optimize a liposomal cyclo(Tyr-Pro) formulation and to assess its antibacterial activity against various Gram-positive and Gram-negative bacteria. Response surface methodology (RSM) using the central composite design (CCD) model was used to optimize liposomal formulations of cyclo(Tyr-Pro) for each of the four bacteria, namely Bacillus cereus, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Percent drug encapsulated and bacterial inhibition were investigated with respect to two independent variables, i.e. lipid composition and cholesterol content. Design Expert 8 was used for the purpose of finding the combination of independent variables that would yield an optimal formulation for each bacterium. The model selected by the software failed to adequately correlate the predicted models to the experimental data. The in vitro experiments showed that the antibacterial activity of liposome-encapsulated cyclo(Tyr-Pro) was superior to that of its free counterpart. Binding maximum or Bmax for the encapsulated compound at concentrations as low as 0.412 mg/ml, was significantly higher than that obtained for free cyclo(Tyr-Pro) which was tested at a concentration of 20 mg/ml. Furthermore, encapsulation of cyclo(Tyr-Pro) into a liposome formulation enhanced its potency. This was evident in the lower IC50 values for the liposomal compound when compared to free cyclo(Tyr-Pro).

Os extratos totais, assim como os compostos fenólicos isolados de diferentes partes de Anacardium occidentale conhecido popularmente no Brasil como cajueiro mostraram atividades antiúlcera e antibacteriana. O objetivo deste trabalho foi a verificação destas atividades nas folhas, estudo farmacobotânico, químico e toxicológico. Para a analise anatômica foram utilizados cortes do terço mediano inferior da lâmina fotiar. Nesta, as epidermes em vista frontal apresentam cutícula estriada, na face abaxial, a epiderme é constituída de células de formato poligonal, com paredes bem justapostas. Na face adaxial, as células são de paredes espessas, ligeiramente onduladas. A mesma é constituída de estômatos de tipo anomocítico e de tricomas glandulares de forma ovóide. O mesófilo é constituído de duas camadas de parênquima paliçádico, espessas, de forma quase regular e de parênquima lacunoso com células de forma irregular, envolvendo os feixes vasculares de nervuras secundarias. Extensões de fibras são observadas no mesófilo. A nervura mediana possui um colênquima desenvolvido e ductos são encontrados no floema assim como no parênquima medular. Drusas são encontradas no parênquima lacunoso assim como no parênquima fundamental e no colênquima. A partir da triagem fitoquímica, da cromatografia em camada delgada, cromatografia liquida de alta eficiência e cromatografia liquida acoplada a espectrometria de massa, verificou-se a presença nas folhas de cajueiro de compostos polifenólicos, particularmente de heterosídeos flavonóidicos. As estruturas de flavonóide que parecem ser mais evidentes, de acordo com a cromatografia liquida acoplada a massa, são principalmente os heterosídeos da quercetina. O extrato etanol 70% liofilizado das folhas do cajueiro foi submetido ao modelo agudo da úlcera gástrica em ratos e a ensaio antibacteriano, ensaiando as linhagens de Staphylococcus aureus ATCC 25923, Escheríchía coli ATCC 35218 e ATCC 25922, Pseudomonas aerugínosa ATCC 27853 e de Campylobacter coli. Na úlcera aguda, a área relativa de lesão ulcerativa foi diminuída de 98% na dose 400mg/kg, em relação ao controle. A partir de um estudo de doses crescentes sobre a inibição de úlcera, a DE50 foi calculada como 150 mg/kg e as doses de extrato maiores ou iguais a 100 mg/kg exibiram uma inibição de lesão ulcerativa melhor que o lansoprazol 30mg. A fração metanólica, que inibiu as ulcerações de 88,20%, deve conter alguns dos princípios ativos da atividade antiúlcera. Quanto ao teste antimicrobiano, foram obtidas concentrações inibitória mínima e bactericida mínima, iguais a 320 µg/mL, particularmente com a linhagem Staphylococcus aureus, a partir do extrato bruto e da sua fração rica em flavonóides. A partir de ensaio de toxicidade aguda em camundongos e ratos, a DL50 do extrato bruto foi considerada superior a 2000 mg/kg. Foi feito um estudo de toxicidade de administração reiterada em 30 e 90 dias. Baseados em analises bioquímicas para avaliação da função renal e da função hepato-biliar, os parâmetros uréia, creatinina, transaminases, proteína total, albumina, colesterol e cálcio tendem a comprovar que o produto é bem tolerado pelo organismo dos ratos. Este fato é também confirmado pelo estudo hematológico e pela histopatologia, não ocorrendo alterações, após administração subaguda do extrato em ratos. O potencial mutagênico foi avaliado através do teste de Ames e do teste do micronúcleo de medula óssea em camundongo. Foi obtido indício de indução de \"frameshift\" e substituição de pares de bases. Na dose de 2000mg/kg, o extrato de cajueiro parece induzir danos nos cromossomos porém, o fenômeno parece ser extremamente inferior (p<0,001) ao efeito clastogênico induzido pela ciclofosfamida, utilizada como agente mutagênico de referência.
Crude extracts as well as phenolics isolated from the bark or the fruit of Anacardium occidentale popularly known as cajueiro in Brazil, showed antiulcer and antibacterial effects. The aim of this work was to verify those effects in the leaf, botanical, chemical and toxicological studies. Ultrastructure of the leaf was carried on. Cross-sections from the third inferior part of the leaf blade were used. Cashew leaf contains uniseriate epidermis with a sub-eperdimic layer, anomocytic stomata and glandular ovoid trichomes on the inferior surface. The mesophyll exhibits two cell layers of palisadic parenchyma and a lacunose parenchyma containing vascular bundles of the secondary nervures. The median nervure contains a developed collenchyma. Several druses of calcium oxalate are present in the fundamental parenchyma, lacunose parenchyma and in the collenchyma. Resin ducts are also observed in the phloem as well as in the medullar parenchyma. Extensions of sclerenchymatous fibres are observed in the mesophyll. By phytochemical analyses using TLC, HPLC-DAD and positive ions LC-ESIMS, we verified the presence of polyphenols in cashew leaves particularly heterosids of flavonoids. From LC-ESI-MS, evident structures of flavonoids seemed to be heterosids of quercetin. Ethanol 70% extract of cashew leaves was used for antiulcer and antibacterial essays. With extract dose 400mg/kg, ulcer lesions induced by HCL/ethanol 60% in rats, decreased about 98%. By a dose-response effect study, ED50 was evaluated about 150 mg/kg. Extract doses higher than 100mg/kg showed potential of lesion inhibition superior to lansoprazol 30mg. Extract methanolic fraction that gave 88,20% of ulcer inhibition likely contains the principie active of the antiulcer effect. Using bacterial strains, Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 35218 and ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and a clinical isolate Campylobacter coli, for antibacterial essay, the ethanolic extract and one fraction rich in flavonoids were only active in S. aureus with MIC and MBC equal to 320 µg/mL. Acute, 30-day and 90-day subacute toxicity studies were carried out. Crude extract DL50 was superior to 2000mg/kg. Based on biochemical analyses for the evaluation of renal and hepato-biliary functions, level of urea, creatinine, transaminases, total protein, albumin, bilirubin, cholesterol and calcium proved that the extract is biologically tolerated by rat organismo This result was also confirmed by studies in hematology and histopathology. Genotoxity was accessed by Ames test in Salmonella typhimurium strains TA97, TA98, TA100, TA102 and bone marrow micronucleus test in mice. The extract exhibited sign of frameshift and base pairs substitution. Extract dose 2000mglkg seemed to induce damage in the chromosomes however; the activity was extremely inferior to the c1astogenic effect induced by ciclophosphamide.

Breast cancer is the most frequently diagnosed cancer in women worldwide.A treatment regime, both effective and safe and can only be achieved once more effective chemotherapeutic agents are discovered or identified. These “drugs” must selectively induce cell death such as apoptosis or necroptosis in the cancer cells. Apoptotic cell death allows a cell to “commit suicide” in genetically- controlled or programmed mechanism(s). The microenvironment of the tumour is important since a nurturing malignant environment is required for tumour maintenance, progression and ultimately the development of metastasis. Due to the correlation of the tumour microenvironment to aggressive tumour progression, emphasis should be placed on the constituents of the tumour’s microenvironment. In recent years, the understanding of intracellular pathways in cancer cells has increased rapidly, contributing to the development of drugs with more specific targets such as growth factors, signalling molecules, cell adhesion proteins, proteases, cell-cycle proteins, modulators of apoptosis and molecules that promote angiogenesis and metastasis. The main aim of this study was thus to identify a few potential or active compounds from a library of synthetically-derived compounds as possible alternative breast cancer treatment candidates.

Resistance of human pathogenic bacterial strains results in selective pressure against known antibiotic. However, plant derived compounds that possess antibacterial potential are currently being investigated for treatment of wound infections in diabetic patients as they are inexpensive and non-toxic. Hence, this dissertation was designed to evaluate two medicinal plants (Brachylaena elliptica and Brachylaena ilicifolia) traditionally used in the treatment of various diseases such as diabetes, and its secondary complications in diabetic patients. The in vitro antioxidant activity of both plants were evaluated using DPPH (1, 1-diphenylhydrazl), ferric reducing power, ABTS (2, 2’-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid), NO (nitric oxide) and H2O2 (hydrogen peroxide) techniques. The antibacterial test and Minimum inhibitory concentration (MIC) was determined by agar dilution method against 5 bacteria strains (Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pyogene, Proteus vulgaris and Proteus mirabilis) infecting wounds in diabetic patients using amoxicillin and ciprofloxacin as positive control. The phytochemical analyses were assessed using standard published methods. Identification of bioactive components in essential oils of both plants were assessed using GCMS. The aqueous and ethanol extracts of both plants were also evaluated to identify bioactive components using LC-MS. The results of the phytochemical analysis revealed the presence of phenols, tannins, flavanoids, flavanols, proanthocyanidins, saponins and alkaloids in both plants. Both plants indicated strong antioxidant activities which might be due to the presence of bioactive compounds. The aqueous and ethanol leaf extracts of both plants demonstrated appreciable broad spectrum activities against these wound pathogens with MIC ranging between 5 and 0.3 mg/ml. The GC-MS analysis of the essential oils of both plants revealed the presence of monoterpenes, oxygenated sesquiterpenes, phenolics and esters. The LC-MS analysis of the aqueous and ethanol leaf extracts of both plants showed that both plants are rich in alkaloids, terpenes, terpenoids, monoterpernoids, and flavanoids. Conclusively, this study has partially justified the ethnomedicinal use of B. elliptica and B.licifolia leaves for the treatment of various diseases, including diabetes and wound infections caused by bacteria in diabetic patients. These may be attributed to the presence of antioxidant compound such as phenols, flavanoids, saponins, tannins, alkaloids and other phytochemical compounds.

Cyclic dipeptides have been well characterized for their multitude of biological activities, including antimicrobial and anticancer activities. Cyclo(His-Gly) and cyclo(His-Ala) have also recently been shown to possess significant anticancer activity against a range of cell lines, despite the limitations of these two molecules with respect to their physicochemical properties. Low Log P results in poor cell permeability which can often be problematic for drugs with intracellular mechanisms of action. It can also results in poor biodistribution, and theoretical Log P values for cyclo(His-Gly) and cyclo(His-Ala) were extremely low making them ideal candidates for inclusion into a nanoparticulate drug delivery system. The aim of this study was therefore to formulate and evaluate liposome-encapsulated cyclic dipeptides that increase the tumour-suppressive actions of the cyclic dipeptides, while showing a high degree of specificity for tumour cells. While liposomes are relatively simple to prepare, inter batch variation, low encapsulation and poor stability are often problematic in their production and this has lead to very few liposomal products on the market. This study aimed at using a comprehensive statistical methodology in optimizing liposome formulations encapsulating cyclo(His-Gly) and cyclo(His-Ala). Initial screening of potential factors was conducted using a 25-1 fractional factorial design. This design made use of two levels for each of the five factors and abbreviated the design to minimize runs. Although not much information is provided by these types of designs, the design was sufficient in identifying two critical factors that would be studies further in a more robust design. The two factors selected, based on the screening study, were cholesterol and stearylamine content. These two factors were then used in designing a response surface methodology (RSM) design making use of a central composite rotatable vii design (CCRD) at five levels (-1.5, -1, 0, 1, 1.5) for each factor in order to better understand the design space. Various factors influenced the measured responses of encapsulation efficiency, zeta potential, polydispersity index, cellular uptake and leakage, but most notable were the adverse effects of increasing stearylamine levels on encapsulations efficiency and cholesterol levels on leakage for both cyclo(His-Gly) and cyclo(His-Ala) liposomes. Optimized formulations were derived from the data and prepared. Fair correlation between the predicted and measured responses was obtained. The cytotoxic activity of the encapsulated cyclic dipeptides were assessed against HeLa and MCF-7 cells and found to have limited improvement in activity. However, modification of the polyethylene glycol (PEG) grafted to the liposome surface in order to target folate receptors showed good benefit in significantly decreasing the IC50 values recorded in all cells lines tested, particularly low folate HeLa cells with the lowest IC50 being recorded as 0.0962 mM for folate targeted cyclo(His-Ala). The results therefore indicate that hydrophilic cyclic dipeptides are ideal candidates for inclusion into targeted drug delivery systems such as liposomes. Key words: Liposomes, cyclo(His-Gly), cyclo(His-Ala), cyclic dipeptides, HeLa, MCF-7, folate receptors, factorial design, response surface methodology (RSM), central composite rotatable design (CCRD).

Infection with Helicobacter pylori has been associated with the pathogenesis of numerous stomach and gastroduodenal diseases that pose threats to public health. Eradicaftion of this pathogen is a global challenge due to its alarming rate of multidrug resistance. Consequently, to find an alternative treatment, the search is increasingly focused on new antimicrobial product from natural sources including honey. Honey has been used as medicine in several cultures since ancient time due to its enormous biomedical activities. Its beneficial qualities have been endorsed to its antimicrobial, antioxidant, anti-inflammatory properties added to its phytocomponents. In this study, the anti-H. pylori activity of South African honeys and their solvent extracts as well as the phytochemicals present in the two most active honeys were evaluated. Agar well diffusion test was used to investigate the antimicrobial activity of six honey varieties obtained from different locations in the country. Subsequently, the honeys were extracted with four organic solvents viz n-hexane, diethyl ether, chloroform and ethyl acetate employed in order of increasing polarity. The antibacterial activity of the different solvent extracts of each honey was evaluated by agar well diffusion; broth micro dilution and time kill assays. Different chromatographic techniques (Thin layer & column chromatography) were employed to enumerate the phytochemical constituents in the most active solvent extracts of Pure Honey (PH) and Champagne Royal Train (CRT); and were identified by gas-chromatography linked mass-spectrometry. Linalool pure compound was equally evaluated for anti-H. pylori activity in a bid to trace the antibacterial agent among the variety of compounds identified. Data were analyzed by One-way ANOVA test at 95% confidence interval. Crude honeys and their solvent extracts demonstrated potent anti-H. pylori activity with zone diameter that ranged from [16.0mm (crude) to 22.2mm (extract)] and percentage susceptibilities of test isolates between 73.3% (crude) and 93.3% (extract). The chloroform extracts of PH and CRT were most active with MIC50 in the ranges 0.01- viii 10%v/v and 0.625-10%v/v respectively, not significantly different from amoxicillin (P> 0.05); and efficient bactericidal activity (100% bacterial cells killed) at 1/2MIC and 4xMIC over different time intervals, 36-72hrs and 18-72hrs respectively. The appearance of bands on the thin layer chromatography (TLC) chromatogram spotted with the chloroform extracts of PH and CRT; and developed with hexane: ethyl acetate: acetic acid (HEA) and methanol: acetic acid: water (MAAW) solvent systems indicated the presence of compounds. Purification of the compounds contained in these extracts over silica gel column yielded numerous fractions which were evaluated for antibacterial activity and purity. PHF5 was the most active fraction with a mean MIC50 value of 1.25mg/mL. Volatile compounds belonging to different known chemical families in honey were identified in all the active fractions obtained from PH. Conversely, only four compounds were identified in the active fractions obtained from CRT hence the non volatile constituents could be of prime relevance with respect to antibacterial activity of this honey. Of novelty was the presence of thiophene and N-methyl-D3-azirdine compounds, essential precursors used for the synthesis of natural products and pharmaceuticals with vital biomedical properties. Linalool demonstrated potent inhibitory (MIC95, 0.002- 0.0313mg/mL) and bactericidal activity (0.0039-0.313mg/mL) against the test isolates. On the other hand, a significant difference was recorded (P < 0.05) in comparing the activity of linalool compound to the fractions. PH could serve as a good economic source of bioactive compounds which could be employed as template for the synthesis of novel anti-H. pylori drugs. However, further studies are needed to determine the non volatile active ingredients in PH and CRT as well as toxicological testing

Najčešća komplikacija nakon ugradnje silikonskih implantata za dojku je kontraktura fibrozne kapsule (KK), koja se normalno stvara oko implantata u sklopu reakcije oko stranog tela. Najozbiljnija komplikacija nakon ugradnje silikonskih implantata za dojku je anaplastični krupnoćelijski limfom koji se javlja isključivo kod pacijentkinja koje imaju ugraĎene implantate (eng. Breast-implant associated anaplastic large cell lymphoma – BIA ALCL). Uzrok nastanka ovih komplikacija ostaje nepoznat. Ustanovljeno je da se KK manje javlja kod implantata koji imaju makroteksturisanu površinu i kod onih koji su presvučeni poliuretanskom penom. S druge strane, BIA-ALCL se češće dijagnostikuje kod pacijentkinja kojima su ugraĎeni upravo makroteksturisani implantati. Subklinička infekcija koja predstavlja odgovor organizma na postojanje biofilma na ugraĎenim implantatima, predstavlja jedan od najznačajnijih etioloških faktora za nastanak KK i BIA-ALCL. Biofilm je konglomerat mirkoorganizama uronjenih u matriks koji ih štiti od dejstva antibiotika i antiseptika. Kako je nemoguće delovati medikamentozno na eradikaciju biofilma, brojni autori daju razne preporuke u cilju izbegavanja kontaminacije implantata tokom operativnog zahvata, a time i formiranja biofilma. Pored brojnih mera, savetuje se i ispiranje džepa u koji će se plasirati proteza kao i same proteze, nekim od antiseptičkih ili antibiotskih rastvora. Do sada ne postoje prihvaćene jasne preporuke o načinu ispiranja različitih implantata, objavljena su samo lična iskustva raznih autora. Ciljevi ovog istraživanja su bili da se ustanovi mogućnost formiranja biofilma četiri različite bakterije (Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa i Ralstonia pickettii) na tri različito teksturisana silikonska implantata za dojku (sa porama veličine 70-150 μm, 50–900 μm i 13 μm) u in vitro uslovima; da se ispita da li ispiranje antisepticima (oktenidindihidrohloridom i povidon jodom), ili antibiotikom (cefuroksimom) ili istovremeno mešavinom povidon joda i antibiotika pre bakterijske kontaminacije sa četiri različite bakterije ima uticaja na formiranje biofilma na tri različito teksturisana implantata za dojke u in vitro uslovima; i da se ispita efekat antiseptika u odnosu na efekat antibiotika na formiranje bakterijskog biofilma na tri različito teksturisana silikonska implantata za dojku. Istraživanje je koncipirano kao prospektivna studija u vidu eksperimenta koji je izveden u Laboratoriji za mikrobiologiju, Instituta za javno zdravlje Vojvodine u Novom Sadu. Za izvoĎenje eksperimenta korišćeni su uzorci tri vrste silikonskih implantata za dojku sa različito teksturisanom površinom, odnosno porama različite veličine: 70-150 μm, 50–900 μm, i 13 μm. Od svakog od navedenih implantata su pravljeni uzorci, sečenjem kapsula implantata na komadiće veličine 1x1 cm. Ukupno je bilo 1440 uzoraka. Na osnovu teksture uzorci su podeljeni u tri grupe: Grupa 1 (pore veličine 70-150 μm), Grupa 2 (pore veličine 50–900 μm) i Grupa 3 (pore veličine 13 μm). Svaka od ovih grupa je dalje podeljena u jednu kontrolnu grupu i po četiri ispitivane grupe. Nakon sterilizacije uzoraka svaka kontrolna grupa je kontaminirana sa po 100μl bakterijskog bujona Staphylococcus epidermidis (n=30), Staphylococcus aureus (n=30), Pseudomonas aeruginosa (n=30) i Ralstonia pickettii (n=30). Ispitivane grupe se bile podeljene prema načinima ispiranja na one u kojima su uzorci prvo ispirani: oktenidin – dihidrohloridom ili povidon jodom ili cefuroksimom ili kombinacijom povidon joda i dva antibiotika, pa potom kontaminirani sa po 100μl bakterijskog bujona Staphylococcus epidermidis (n=30), Staphylococcus aureus (n=30), Pseudomonas aeruginosa (n=30) i Ralstonia pickettii (n=30). Po završenoj kontaminaciji, uzorci su se inkubirali na temperaturi od 37°C u trajanju od 96h, čime su stvoreni uslovi za formiranje biofilma. Nakon inkubacije, svaki pojedinačni uzorak je uronjen u sterilan tripton soja bujon, izlagan soničnoj energiji u trajanju od 1minuta i zatim vorteksiran 1 minut, čime je omogućeno odvajanje nastalog biofilma od implantata. Za ispitivanje sposobnosti formiranja biofilma korišćena je modifikovana tehnika sa mikrotitar pločom po Stepanoviću. Rezultati su pokazali da sve četiri ispitivane bakterije S. epidermidis, S. aureus, P. aeruginosa i Ralstonia pickettii statistički značajno više stvaraju biofilm na implantatima sa porama veličine 50–900 μm u odnosu na pore 70-150 μm i u odnosu na pore veličine 13 μm. Biofilm se statistički značajno više stvara na porama veličine 70-150 μm u odnosu na pore 13 μm. Jedini izuzetak je Pseudomonas aeruginosa kod kojeg ne postoji statistični značajna razlika u produkciji biofilma na teksturisanim implantatima sa porama veličine 70-150 μm u odnosu na one sa porama 13 μm. TakoĎe, sve četiri ispitivane bakterije statistički značajano manje stvaraju biofilm nakon ispiranja povidon jodom, oktenidin-dihidrohloridom ili rastvorom antibiotika u sve tri grupe implantata, u odnosu na površine koje nisu ispirane. Izuzetak je S. epidermidis u Grupi 3 kod kojeg nije utvrĎeno statistički značajno manje formiranje biofilma nakon ispiranja oktenidin dihidrohloridom u odnosu na neispiranje. Cefuroksim je bio efikasniji u sprečavanju formiranja biofilma sve četiri ispitivane bakterije u odnosu na neispiranje u Grupi 1, kao i za S. epidermidis i Ralstoniu Pickettii u Grupi 2. Cefuroksim se nije pokazao statistički značajno efikasnim u sprečavanju formiranja biofilma S. aureus i P. aeruginosa u Grupi 2, kao ni kod jedne bakterije u Grupi 3. Dalje je dokazano da su antiseptici (oktenidin-dihirohlorid i povidon jod) kao i mešavina povidon joda i dva antibiotika (cefuroksim i gentamicin), statistički značajno efikasnji od ispiranja samo antibiotikomcefuroksimom u smanjenju formiranja biofilma sve četiri ispitivane bakterije kod sva tri ispitivana, različito teksturisana silikonska implantata. Rezultati su pokazali da je ispiranje povidon jodom statistički značajno efikasnije u prevenciji stvaranja biofilma kod skoro svih ispitivanih bakterija od ispiranja oktenidin- dihidrohloridom u sve tri grupe implantata. Statistički značajna razlika nije utvrĎena u prevenciji stvaranja biofilma Staphylococcus aureusa kod sve tri grupe implantata prilikom ispiranja povidon jodom u odnosu na oktenidin- dihidrohlorid, kao i kod Ralsotnia pickettii u Grupi 2. Na osnovu rezultata ove studije, preporuka je da se koriste mikroteksturisani implantati kao i da se oni, pre ugradnje isperu povidon jodom ili mešavinom povidon jod i dva antibiotika (cefuroksim i gentamicin), u cilju prevencije stvaranja biofilma, a time i postoperativnih komplikacija koje mogu nastati nakon ugradnje implantata.
The most common complication after breast implant surgery is contracture of capsule, which is normally formed around implants as part of foreign body reaction. The most sincere complication after this kind of surgery is breast implant associated anaplastic large cell lymphoma (BIA-ALCL). The cause of these complications is still unknown. It is evident that capsular contracture (CC) is seen less frequently in patients with macro-textured implants and in those with implants covered with polyurethane foam. On the other hand, BIA-ALCL is diagnosed more frequently in patients with those, macro-textured implants. Subclinical infection, defined as an response of organism on presence of biofilm on the implant, is considered to be one of the most important etiologic factors for CC and BIA-ALCL. Biofilm is a conglomerate of microorganisms immersed into matrix, which protects them from influence of antibiotics and antiseptics. As it is impossible to eradicate biofilms with medicaments, many authors suggest different steps in order to avoid contamination of the implant during the operation and therefore, prevent the formation of biofilm. Among many tips, it is recommended to irrigate the pocket for breast implant and the implant itself, with some antiseptic or antibiotic solution. Up till now, there is no agreed consensus on the type of irrigation for different implants. Only personal experiences of a few authors have been published. Aims of this research were: to establish the possibility of biofilm formation of four different bacteria (Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa and Ralstonia pickettii) on three differently textured breast implants (with pore diameter of 70-150 μm, 50–900 μm and 13 μm) in vitro; to examine whether the irrigation of implant with antiseptics (povidone iodine and octenidine dihydrochloride), antibiotics (cefuroxime) or mixture of povidone iodine and two antibiotics, before the contamination with bacteria, has an influence on the incidence on biofilm formation on three differently textured implants; and to examine the effect of antiseptics in contrast to the effect of antibiotics on biofilm formation on three differently textured breast implants. The study was conducted as a prospective research that took place at the Laboratory for microbiology, at the Institute of public health of Vojvodina in Novi Sad. For the experiment, three types of silicone breast implants were used with different pore sizes: 70-150 μm, 50–900 μm and 13 μm. Samples were made by cutting each of these types of implants into pieces sized 1x1cm. There were 1440 samples in total. According to texture, samples were divided it three groups: Group 1 (pore size 70-150 μm), Group 2 (pore size 50–900 μm) and Group 3 (pore size 13 μm). Furthermore, each of these groups was divided in one control and four test groups. After sterilisation of samples, every control group was contaminated with 100μl of bacterial broth of Staphylococcus epidermidis (n=30), Staphylococcus aureus (n=30), Pseudomonas aeruginosa (n=30) and Ralstonia pickettii (n=30). Tested groups were divided according to type of irrigation into those where samples were firstly irrigated with either: octenidine dihydrochloride of povidone iodine or cefuroxime of mixture of povidone iodine with two antibiotics, and after the irrigation, contaminated with 100μl bacterial broth of Staphylococcus epidermidis (n=30), Staphylococcus aureus (n=30), Pseudomonas aeruginosa (n=30) and Ralstonia pickettii (n=30). After contamination, samples were incubated on 37°C for 96h, which created excellent conditions for biofilm formation. After incubation, each sample was dipped into sterile tripton soy broth, and then exposed to sonic energy for 1 minute and vortexed for 1 minute, which made biofilm separate from the implant. For testing the capability of biofilm formation, modified technique with microtitar plates described by Stepanović was used. Results show that all four examined bacteria S. epidermidis, S. aureus, P. aeruginosa and Ralstonia pickettii form more biofilm on implants with pore sizes 50–900 μm compared to implants with pore size 70-150 μm and those with 13 μm. Statistical significance was found in biofilm formation on implants with pores 70-150 μm compared to implants with pores 13 μm. Furthermore, all four examined bacteria form statistically less biofilm after the irrigation with any of used solutions: povidone iodine, octenidine dihydrochloride, antibiotic solution of mixture of povidone iodine and two antibiotics, in all three groups of implants compared to surfaces that were not irrigated. The exception is S. epidermidis in Group 3, where no statistical significance was found on biofilm formation after the irrigation with octenidine dihydrochloride compared to non-irrigation. Cefuroxime was more efficient in biofilm prevention for all four tested bacteria compared to non-irrigation in Group 1 and for S. epidermidis and Ralstonia pickettii in Group 2. There was no statistical significance found in prevention of S. aureus i P. aeruginosa biofilms when irrigating with cefuroxime in Group 2, as well as for all tested bacteria in Group 3. Furthermore, it was verified that antiseptics (octenidin dihydrochloride and povidone iodine) and mixture of povidone iodine and two antibiotics (cefuroxime and gentamycin), were statistically more efficient in biofilm prevention of all four examined bacteria in all groups of implants, compared to irrigation with antibiotic-cefuroxime alone. Results show that irrigation with povidone iodine is statistically more efficient in biofilm prevention of almost all examined bacteria compared to irrigation with octenidine dihydrochloride in all groups of implants. There was not found any statistical significance in prevention of Staphylococcus aureus biofilm when irrigating with povidone iodine compared to octenidine dihydrochloride in all groups of implants, and also in biofilm prevention of Ralsotnia pickettii in Group 2. According to results of this research, it is recommended to use micro-textured implants and to irrigate them with povidone iodine or mixture of povidone iodine and two antibiotics (cefuroxime and gentamycin) prior the implementation, in order to prevent biofilm formation which is most probable cause of postoperative complications after implant surgery.

Protein translocation is essential for bacterial survival and the most important translocation mechanism in bacteria is the secretion (Sec) pathway. Thus targeting Sec pathway is a promising strategy for developing novel antibacterial therapeutics. We report the design, syntheses, mechanistic studies and structure-activity relationship studies using HQSAR and 3-D QSAR Topomer CoMFA analyses of 4-oxo-5-cyano thiouracil derivatives. In summary, introduction of polar group such as –N3 and linker groups such as –CH2-O- enhanced the potency as well as logP and logS several fold. We also report the discovery, optimization and structure-activity relationship study of 1,2,4-triazole containing pyrimidines as novel, highly potent antimicrobial agents. A number of inhibitors have been found to inhibit microbial growth at high nanomolar concentrations.

The bacterial cell envelopes possess a complex multilayered architecture exhibiting unique properties evolved to regulate interactions with the external environment and molecules with antimicrobial properties. A molecular understanding of the interactions of external molecules with the bacterial envelope will aid in the development of novel antibacterial formulations. Using detailed molecular models of the bacterial cell envelope, we have carried out molecular dynamics simulations and free energy computations to gain insights into the interactions of membrane targeting antibacterials and surfactants. We have elucidated the molecular basis for the interaction and transport of antibacterial therapeutics with both the Gram-negative inner membrane (IM) and outer membrane (OM) as well as the periplasmic peptidoglycan cell wall. Free-energy computations reveal the presence of a barrier in the core-saccharide region of the OM for the translocation of thymol a naturally occurring antibacterial while the external O-antigen region is easily traversed. In contrast, thymol spontaneously inserts into the IM and lipid diffusivities show a distinct increase in the presence of thymol. The all-atom simulations for these asymmetric bacterial membranes are challenging due to the large number of atoms involved in these models. Therefore, coarse-grained MARTINI models are preferred for these systems. We have compared the all-atom (CHARMM36) and coarse-grained (MARTINI) models of the IM, periplasmic peptidoglycan (PGN) and OM. The structural and barrier properties of the membrane were contrasted. Our results indicate that the MARTINI models accurately capture insertion free energies for small molecules and other structural properties with all-atom models of both the IM and PGN layer. We have also illustrated the lipid composition effects on the IM properties and affirmed the need to employ accurate all atom models for these membranes. Surfactants, with their ability to solubilize lipids, are another class of widely used antibacterial agents. We observe that the PGN layer does not offer a barrier to isolated surfactant molecules, however the passage of surfactant aggregates were restricted. We also observed greater changes to the IM structural and mechanical properties in the presence of laurate and rationalize differences in the efficacy of these surfactants with different aggregation properties, chain lengths, and electrostatic interaction with PGN. In the last part of the thesis, we have assessed the ability of ve coarse-grained MARTINI 1, 2-dipalmitoylsn- glycero-3-phosphocholine (DPPC) membranes to capture the ripple phase in membranes. Our study illustrates that the presence of the partly interdigitated ripple-like states are a strong function of system-size and occur as kinetically trapped structures in smaller lipid patches. The present MARTINI force elds will require additional re-parametrization to capture the ripple phase. Coupled with free energy computations our in silico study reveals lea etresolved insertion properties in bacterial membranes allowing one to assess the ability of naturally occurring small molecules such as thymol and surfactants to penetrate various membrane components. Molecular insights gained from our study can potentially be used in the design of novel antibacterial formulations to improve the efficacy of therapeutics and disinfectants to eventually combat the rise of resistant bacterial strains.

Increasing bacterial drug resistance and the emergence of dangerous resistant pathogens like methicillin-resistant Staphylococcus aureus is driving an urgent need to develop new antibiotics. Antimicrobial peptides (AMPs) and metals are two classes of antibacterial agents being explored as novel therapeutics. AMPs are produced as a part of innate immune system of living organisms and have broad spectrum activity and a bactericidal effect making bacteria less able to develop resistance., Metals are one of the oldest antibacterial agents known to humans. Notably, silver is very effective, and although its exact mode of action/s is unclear its ability to bind to a variety of enzymes is likely important. This project aims to investigate whether the coordination of silver to AMPs can create a synergistic antibacterial agent. To achieve this, AMPs, based on their potential to bind Ag(I), were selected from large AMP databases available online. Three AMPs, latarcin 3b, pleurain R1, tigerinin1, were selected. Further two Ag(I)-binding neuropeptides having properties consistent with antibacterial activity were also investigated. These were the tachykinins Neurokinin B, Substance P. Finally, Substance P was modified to include a methionine at its N-terminus (M1 Substance P) to generate a predicted high-affinity Ag(I)-binding site. The physiochemical properties of all the peptides were assessed using the R computational tool and these were related to potential antibacterial potential. Neurokinin B and Substance P have previously been shown to bind Ag(I), and the ability of the remaining peptides to coordinate Ag(I) was assessed using NMR and electronic spectroscopy. All but pleurain R1 and tigerinin1 could coordinate Ag(I), and further investigation of pleurain indicated that the lack of Ag(I)-binding was due to disulphide-bond formation. The Peptide-Ag(I) complexes were then studied for their antibacterial properties against gram negative bacteria using percentage inhibition and time-kill analysis. The results of this analysis showed that two complexes, latarcin 3b-Ag(I), and M1SP-Ag(I) displayed synergistic activity. Finally, the cellular location of silver after cultures were treated with these complexes was determined. These results show that silver alone is located mainly in the periplasm, but coordination to the peptides traps the metal in the membrane. This suggests that the synergistic effect is due to improved membrane-lytic activity. It can be concluded that the Peptide-Ag(I) complex can hold potential as next-generation antibacterial agents.

Submitted in fulfillment of the requirements of the degree of Master in Technology, Department of Biomedical Technology and Clinical Technology, Durban University of Technology, Durban, South Africa, 2016.
Introduction In Africa, use of phytotherapy for treatment of diabetes mellitus is a common form of practice. Considering the increasing burden of non-communicable diseases in South Africa efforts are directed at simple, cost effective, non-hazardous and efficient methods to treat cancer, cardiovascular diseases and diabetes. The role of phytonanotherapy is an attractive proposition for advancing new therapies. Metal nanoparticles are a possible means for delivery of such therapies. However, this requires investigation on interactions, mechanisms and therapeutic efficacy upon co-administering ethnobotanicals with metal nanoparticles and existing drug therapy in human beings. Aim The primary aim of the study was to test the in vitro antidiabetic and antibacterial activity of Ocimum sanctum (leaf extracts and flower extracts), Ocimum basilicum (leaf extracts and flower extracts), and a combination of the leaf extracts of both, and to observe whether any antidiabetic and antibacterial activity was enhanced in due to phyto-synthesised bimetallic gold-silver (Au-Ag) nanoparticles and silver nanoparticles. Methods Aqueous and ethanol extracts of O. sanctum and O. basilicum leaf and flowers alone and combined (leaf + flower) were prepared using hot vs cold water extraction techniques and 60% and 70% ethanol as polar solvents. A simple, rapid, cost effective and reproducible green chemistry method synthesised alloyed bimetallic (Au-Ag) nanoparticles using O. basilicum leaf and flower aqueous extracts and prepared silver nanoparticles (AgNps) using O. basilicum and O. sanctum leaf aqueous extracts singly and in combination (O. sanctum + O. basilicum). The size, shape and elemental analysis of the nanoparticles was carried out using UV-Visible spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy coupled with energy-dispersive X-ray (SEM-EDX), dynamic light scattering (DLS) and zeta potential. Fourier transform infrared spectroscopy (FT-IR) supported by gas chromatography mass spectroscopy (GC-MS) identified the bio-capping agents. Antidiabetic carbohydrate metabolising enzymes, α-amylase (porcine) and Bacillus stearothermophilus α-glucosidase as models tested the in vitro inhibitory potential of the aqueous and ethanol plant extracts and the phyto-synthesised (Au-Ag) bimetallic and AgNps. In addition, the study investigated the antibacterial potential for the aqueous plant preparations and their respective phyto-synthesised bimetallic and AgNps against the bacterial species Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Salmonella species and Pseudomonas aeruginosa compared to gentamycin and vancomycin. Results Bimetallic nanoparticles (synthesised from leaf and flower aqueous extracts) displayed inhibitory activity that showed uncompetitive inhibition (leaf extract), and non-competitive inhibition (flower extract) of α-amylase and competitive (leaf extract) and uncompetitive inhibition (flower extract) of α-glucosidase. Bimetallic nanoparticles were higher in inhibitory activity than acarbose and the crude O. basilicum ethanol and aqueous leaf and flower extracts. In the antibacterial analysis, bimetallic nanoparticles derived from O. basilicum leaf showed inhibition against Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa and were greater in activity compared to the crude aqueous leaf extract from O. basilicum. The in vitro inhibitory effect of AgNps derived from O. sanctum and AgNps derived from O. basilicum on both enzymes was higher in activity than acarbose and their respective crude extracts. However, in combination (O. sanctum + O. basilicum), the derived AgNps appeared to be a less potent inhibitor of α-amylase and α-glucosidase enzyme and was lower than acarbose. AgNps synthesised from the combination of O. sanctum and O. basilicum showed the highest percentage inhibition against Bacillus stearothermophilus α-glucosidase, and AgNps derived from O. sanctum and AgNps derived from O. basilicum displayed competitive type of inhibition. In the antibacterial analysis, AgNps derived from the various extracts showed zones of inhibition against the Gram negative and Gram positive bacterial test strains. However, AgNps synthesised from the O. sanctum leaf extract showed higher inhibition against Escherichia coli than the positive control gentamycin and higher inhibition against Staphylococcus aureus compared to vancomycin. In addition, AgNps from O. sanctum leaf extract displayed inhibition against Bacillus subtilis, Pseudomonas aeruginosa and Salmonella species, thus representing the highest antibacterial potential. Conclusion The results demonstrate the possibility of synthesis of stable silver and bimetallic nanoparticles of Ocimum sp. The synthesised silver nanoparticles and first time synthesis of bimetallic (Au-Ag) nanoparticles displayed enhanced antihyperglycaemic properties compared to their respective crude extracts and, therefore, show promising effects in lowering postprandial hyperglycaemia in diabetic patients with dual potential for antibacterial treatment. However, the antidiabetic and antibacterial effect will need to be further affirmed in a clinical context. Medicinal plants with therapeutic value may create a new platform for further research to explore the potential for herbal medicine and nanoscience as effective biomedical and industrial applications, and for improving existing drug delivery systems in diabetic patients. Investigations into the cytotoxicity of these extracts and phytosynthesised nanoparticles is recommended.
M

Thesis (M.Sc. (Microbiology)) -- University of Limpopo, 2015
Antioxidants play an important role in living organisms to control level of free radicals and other reactive molecules in the body to reduce oxidative damage. Synthetic antioxidant compounds are used in food industries as food additives to boost our immune systems. These compounds are associated with a number of critical side effects including liver damage and carcinogenesis. Scientists are also concerned about microorganisms that have developed resistant genes against current antibiotics used in hospitals. The aim of the study was to isolate and characterize bioactive compounds from Ricinus communis leaves with activity against Staphylococcus aureus (ATCC 29213), Enterococcus faecalis (ATCC 29212), Escherichia coli (ATCC 25922) and Pseudomonas aeruginosa (ATCC 27853). Consequently, medicinal plants are studied and considered for their efficacy and safety, because they possess bioactive compounds with various biological activities. Leaves of R. communis were collected at the University of Limpopo, Turfloop campus in Limpopo province, South Africa. The leaves were dried and milled to a fine powder. A number of trial extraction methods were employed using various solvents of different polarities on a fine powder leaves to identify the best extraction method. Plant extracts were analyzed by thin layer chromatography (TLC) developed in four mobile phases. To detect separated phytochemical compounds, TLC plates were sprayed with vanillin- sulphuric acid in methanol and heated at 110oC for optimal colour development. Qualitative antioxidant activity was determined by using 2, 2–diphenyl-1-picrylhydrazyl (DPPH) assay on TLC plates. Quantitative antioxidant activity was determined by measuring percentages scavenging activity of DPPH and 2, 2’-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) free radical molecules by plant extracts. Antibacterial activity of all extracts was quantified by a serial microbroth dilution method while bioautography was used in qualitative analysis of the active compounds. Cytotoxicity effect of R. communis extracts was evaluated using tetrazolium-based calorimetric assay on human Caucasian skin fibroblast (Bud-8) cell line. Anti-inflammatory activity was assessed using phagoburst kit on Raw 264.7 macrophages cell line. Pure compounds were subjected to nuclear magnetic resonance spectroscopy for 1H, 13C and DEPT experiments to elucidate structures of compounds. 2 During extraction process, methanol was the best extractant, extracting greater amount of extracts than any of the other solvents. Serial exhaustive extraction method was selected as the best extraction method for extracting compounds from ground plant materials. In quantitative antioxidant assays, chloroform and methanol extracts had highest percentage scavenging activity against DPPH free radicals compared to other extracts and vitamin C. Methanol extract had the highest percentage scavenging activity of ABTS free radicals and minimum percentage scavenging activity was in hexane extract. Acetone, ethyl acetate and ethanol extracts showed strong antioxidant activity against DPPH free radicals in qualitative antioxidant assay on TLC plates. In quantitative antibacterial assay, crude extracts showed lowest minimum inhibitory concentration value of 0.13 mg/ml against all tested organisms and the highest was 1.05 mg/ml. Hexane extracts revealed potent antibacterial activity against all tested microorganisms on bioautograms. Hexane and acetone extracts also revealed anti-inflammatory activity and have ability to reduce oxidative stress. In cytotoxicity effect of plant extracts, Methanol extracts had lethal concentration for 50% of the cells (Lc50) of 784 μg/ml on Human Caucasian skin fibroblast (Bud-8) cell line while hexane extracts had Lc50 of 629 μg/ml. Plant extracts with high Lc50 are low toxic to normal cell line and preferable to work with for drug development. Bioassay-guided fractionations results in successful isolation of three antioxidant and two antibacterial compounds from R. communis using column chromatography. Isolated compounds were tested for their biological activities using qualitative DPPH assay on TLC plates for antioxidant activity and bioautography for antibacterial activity. Antioxidant compounds showed strong antioxidant activity after spraying with DPPH in methanol and antibacterial compounds showed less activity compared to the crude extracts. The study suggests the use of crude extracts to fight against pathogenic microorganisms compared to pure compounds. Compound 4 was successful identified as the mixture of stigmasterol and β-sitosterol. The present study recommends the use of R. communis leaves as the potential source of antioxidant, antibacterial and anti-inflammatory compounds. The study serves as a scientific proof for use of this plant in traditional medicine for treatment of various ailments.

Silver nanoparticles have become common place today due to their antimicrobial properties however they have become particularly popular due to their potential to kill multi-resistant (MR) bacteria. Silver nanoparticles have shown promising results as a solution to the problem of antibiotic resistance. However, little is known about their spectrum of antimicrobial activity, their mode of action and their most effective size and morphology. Furthermore, there has been limited research into the effectiveness of silver nanoparticles over time, their leakage into the environment, their effect on natural ecosystems and their potential persistence in the environment. The aim of this project was to develop a silver nanoparticle with proven antimicrobial properties, and to gain understanding of the aging process and possible persistence. This was conducted by synthesising and characterising silver nanoparticles using different synthetic methods, determining their antimicrobial properties and evaluating changes in size, morphology and antimicrobial effects after aging. Particle morphology and size was determined via Ultraviolet–visible spectroscopy (UV-vis) and Scanning Electron Microscopy (SEM). Minimum Inhibitory Concentrations (MIC) and Minimum Bactericidal/Fungicidal Concentration (MBC/MFC) assays were performed to determine the extent of antimicrobial properties. The silver nanoparticle samples were then aged for a week under ambient conditions and again characterised by UV-vis, SEM, and MICs were determined. Nanoparticles synthesised by the heat reduction method produced a highly effective bactericidal and antifungal effect but showed stability making them potentially harmful to the environment. Alternatively, the chemical reduction method produced particles which showed antimicrobial properties against Gram-negative bacteria, were short lived and therefore providing a lower environmental impact. The results of this study have demonstrated the importance of understanding and considering the synthetic method and how it affects the associated silver nanoparticle aging process.

Indiana University-Purdue University Indianapolis (IUPUI)
The purpose of this study was to investigate the antibacterial efficacy of 0.12-percent and 2.0-percent chlorhexidine gluconate (CHX) on eliminating Enterococcus faecalis from dentinal tubules, and whether this antibacterial effect was enhanced by heat. To date there have been no published articles that describe the heating of 2.0-percent CHX and its antimicrobial efficacy and clinical relevance towards E. faecalis within dentinal tubules in root canal systems. Ninety-five human extracted, single rooted, maxillary, anterior teeth were used to prepare dentin disk specimens. After proper sterilization, a 2.5-mm ISO-sized diameter lumen was prepared, and then the canals were filled with brain-heart infusion (BHI) broth infected with E. faecalis. The BHI was removed and the specimens in equally divided groups were rinsed with sterile saline and filled with saline, or 0.12 percent CHX or 2.0 percent CHX at ambient temperature (24°C) or experimental temperature (46°C) and incubated at oral temperature (37°C) or the experimental temperature (46°C), respectively. The specimens were frozen to -70˚C and pulverized in liquid nitrogen. Serial dilutions were prepared of 1:100 and 1:1000 and spiral plated on BHI agar plates in duplicate. They were incubated, and the number of bacterial colonies was recorded 24 hours later for data analysis. A two-way analysis of variance (ANOVA), with factors for solution, solution temperature, and the solution-by-temperature interaction was used to determine antibacterial efficacy. Pair-wise comparisons between groups were examined for significance using the Fisher’s Protected Least Significant Differences Method. The E. faecalis CFU were log-transformed to satisfy the assumptions required for the ANOVA. The results of this investigation demonstrated no statistically significant difference with the addition of heat to either test irrigation solution regarding the elimination of E. faecalis from dentinal tubules within the root canal system. There was a statistically significant difference in the antibacterial efficacy of CHX against E. faecalis in comparison with the concentration tested. A higher concentration of 2.0-percent CHX demonstrated a significantly higher antibacterial efficacy against E. faecalis compared with 0.12-percent CHX, and likewise with the saline control. It can be concluded that the use of a higher concentration of 2.0-percent CHX is advantageous as a final irrigation solution after copious amounts of NaOCl and EDTA have been utilized for effective antimicrobial efficacy and substantivity.

Antibiotic resistant strains of bacteria are a serious threat to human health. With increasing antibiotic resistance in common human pathogens, fewer antibiotics remain effective. Staphylococcus aureus is a pathogenic bacterium of particular concern to human health as it has developed resistance to many of the currently used antibiotics leaving very few remaining as effective treatment. Alternatives to current conventional antibiotics are needed to allow for the continued treatment of bacterial infections. In addition, a deeper understanding of the characteristics of antibiotic resistant bacteria is needed to allow for an increased ability to properly treat them and to potentially identify targetable changes. To address these two issues, this study aimed at investigating antibacterial activity of an anti-scabies permethrin cream, and examining the lipidomics, proteomics, cell wall thickness and whole-cell surface charge of methicillin sensitive S. aureus (MSSA) and methicillin resistant S. aureus (MRSA). The permethrin cream was found to contain both 5% permethrin and 0.3% formaldehyde and so both were tested alone and in combination for antibacterial activity against MSSA and MRSA. This was done using antimicrobial susceptibility experiments and time-kill assays with viable counts determined using a drop plate method. In addition, any effect of permethrin on cell morphology was investigated using scanning electron microscopy. While permethrin was found to have little effect on bacterial growth and morphology, formaldehyde was found to be capable of inhibiting the growth of both MSSA and MRSA at concentrations found in the permethrin cream as well as four times lower (0.07%) and at 0 hours. Formaldehyde therefore represents a potential alternative treatment for infections with antibiotic resistant bacteria. But for it to be used in this manner the risks associated with it will need to be investigated as there is a lack of literature relating to the effect of dermal application of formaldehyde in humans. The results presented here show that permethrin is a poor inhibitor of bacterial growth but formaldehyde rapidly kills MSSA and MRSA and therefore may serve as an alternative to conventional antibiotics. Additionally, individual strains of MSSA and MRSA were shown to be able to differ from each other beyond the characteristic antibiotic resistance changes. Continued work on this would benefit from examining a wider range of strains and including mutant strains and/or antibiotic challenge to understand how MRSA can change beyond the well characterised expression of penicillin binding protein 2A. This would allow for a deeper understanding into the functioning of S. aureus cells and this can be used to better develop treatments for infections with antibiotic resistant strains of bacteria.