Massey Documents by Type

Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294

Browse

Has files: YesSubject: search.filters.subject.Anti-infective agents

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Antimicrobial potential of Clostridium and closely related species derived from farm environmental samples : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatū, New Zealand
    (Massey University, 2021) Weligala Pahalagedara, Amila Srilal Nawarathna
    The exploration of antimicrobial compounds from natural sources such as bacteria, has been fast tracked by the development of antimicrobial resistance to existing antimicrobials and the increasing consumer demand for natural food preservatives. So far, antimicrobial discovery has been biased towards aerobic and facultative anaerobic bacteria and fungi. Strict anaerobes such as Clostridium species have not been thoroughly investigated for their antimicrobial potential. The objective of the current study was to evaluate the antimicrobial potential of Clostridium and closely related species against bacteria associated with food spoilage, food safety, and human health. Tests on culture media inoculated with Clostridium and closely related species from farm samples (conditioned media/CMs) showed various degrees of antimicrobial activity. Farm 4 soil conditioned medium (F4SCM) showed potential for further investigation in the search for potent antimicrobials with its promising antimicrobial activity. Bacterial isolates (FS01, FS2.2, FS03, and FS04) belonging to Clostridium and closely related spp. associated with F4SCM showed antimicrobial potential as evident by culture-based and genome-based methods. F4SCM and FS03CM (CM prepared from FS03) metabolomes showed the presence of several putative antimicrobial metabolites. Among them, 2-hydroxyisocaproic acid (HICA) showed antimicrobial activity against a wide range of bacteria associated with food spoilage and safety indicating its potential as a bio-preservative agent in food products. The cell cytoplasmic membrane is a likely target of the HICA’s antimicrobial activity. Overall, this study demonstrates that anaerobic bacterial species, Clostridium, and closely related species can produce antimicrobial metabolites, that have potential applications in food preservation and human health. The knowledge obtained in this study will help future investigations to identify and characterize antimicrobials from these Clostridium and closely related bacteria and expands the understanding of the potential to produce antimicrobial compounds from the genus Clostridium and closely related species.
  • Thumbnail Image
    Item
    Antibacterial properties of diterpenes and their derivatives : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Microbiology at Massey University
    (Massey University, 1998) Nicolson, Kirsty
    Totarol is a diterpene isolated in large quantities from P. totara and a range of other plants, that has been shown to possess significant antibacterial activity against Gram positive bacteria. It has not been possible to unequivocally determine the mode of action by which this activity occurs. This research aimed to determine the mode of action of the diterpene and study a range of derivatives to elucidate a structure-function relationship for the diterpene to enable directional synthesis of future derivatives possessing increased activity and bioavailability. The antibacterial activity of totarol and 29 derivatives was tested against H.pylori and S. aureus, two significant human pathogens,as representative Gram negative and Gram positive bacteria. Four compounds were found to possess significant activity against S. aureus, both MRSA and MSSA, although no significant activity was observed against H. pylori. The ability of the derivatives to potentiate the activity of existing β-lactam antibiotics such as methicillin was also investigated for MRSA and E. coli. Seven compounds including totarol were found to potentiate methicillin, one 256-fold, although no potentiation activity was exhibited against E .coli. The incorporation of radiolabelled precursors was used to investigate the effect of totarol on the synthesis of three macromolecules, DNA, protein and peptidoglycan, in MRSA. No primary inhibition was detected, indicating that the mode of action of the diterpene was not inhibition of synthesis of any of these macromolecules. The effect of totarol on the cellular respiration of MRSA was also investigated, showing 70 % inhibition of respiration at MIC levels, and complete inhibition of respiration at five times that concentration. It was therefore concluded that this was the most likely primary antibacterial effect of the compound. The effect of totarol on the production of PBP 2a, an important protein in theβ- lactam resistance mechanism of MRSA, was also investigated using a novel, non-radioactive labelling procedure to detect the protein. However, although a variety of strategies were employed to detect the protein, none were successful, and the experiment set aside until the arrival of anti-PBP 2a antibody for use in another strategy. Future work on this project that could be undertaken includes determination of the effect of the derivatives on cellular respiration under potentiation conditions, determination of the component(s) of the respiratory chain affected by totarol, and the investigation of the effect of the diterpene on PBP 2a production and function using antibody to detect the protein.
  • Thumbnail Image
    Item
    The potential use of hen egg white lysozyme as an antimicrobial agent in foods : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology at Massey University
    (Massey University, 1995) Rushizha, Edgar
    The potential use of lysozyme as an antimicrobial agent in foods was investigated in model food systems(brainheart infusion broth) using factorial designed experiments and in mussel and cottage cheese food systems. Optical density or absorbance was used as a tool to monitor the growth response of Listeria monocytogenes and C. tyrobutyricum in brain heart infusion broth under the combined influence of pH(5.5, 6.5), lysozyme (0.2mg/ml, 3mg/ml) and different chelating agents(ethylene diaminetetraacetic acid(EDTA), glycine, gluco delta lactone(GDL), citric acid, sodium phosphate dibasic(SPDB) and sodium hexametaphosphate(SHMP)(10mM, 25mM). Using 2 3 full factorial design experiments, the yield of the organisms (expressed as the area under the curve of a plot of change in optical density at 600nm vs time) was taken as the quantitative response variable for each treatment. These yield values were then used for (a) statistical analysis to determine which of the single or interactive factors tested significantly reduced the yield, (b) formulation of a mathematical regression equation which could be used to predict microbial growth within the limits of the factors studied. Diagnostic plots were constructed to evaluate further how well the statistical model fit the observed yield values. Plots of residuals versus predicted yield values appeared to suggest that a transformation of the response would improve the fit of the models. No other serious reservations were suggested by the diagnostic plots. Goodness of fit of the models was also evaluated by the R-squared values. Significant two-way and three-way interactions between lysozyme, pH and EDTA, GDL, citric acid and glycine were exhibited. Response surface methodology(RSM) was used to (a) characterize the response of L. monocytogenes to variation in treatment combinations and (b) show non-linearity of models(or interaction of factors). Generally yield was minimal in treatment where pH was low, with high lysozyme and chelator. Based on equal molar concentrations, the antimicrobial activity of the different chelating agents was in the order EDTA > GDL > citric acid > glycine > adipic acid > SHMP > SPDB. The same ranking was true for the degree to which each chelating agent enhanced lysozyme activity. Based on broth culture studies, the chelating agents EDTA, GDL, glycine, citric acid and adipic acid were demonstrated to have potential for use as antimicrobial agents in combination with lysozyme in food systems. Results of a 2 5 factorial design indicated that the 5 factors, lysozyme, GDL, pH, inoculum level and temperature were important in the inhibition of L. monocytogenes. Results of the broth culture studies gave a good reflection of the survival of L. monocytogenes in the food system. The variable combinations interacted to decrease the growth of L. monocytogenes and extended the lag phase duration. However C. tyrobutyricum was more tolerant to the different treatment combinations other than EDTA. A study of protein interference demonstrated that the antimicrobial activity of the lysozyme-GDL preservation system was not inhibited by the presence of proteins. The food system study demonstrated that the lysozyme-GDL treatment combination has potential for use as a preservative in refrigerated low pH ready-to-eat foods. The susceptibility of L. monocytogenes to lysozyme-GDL treatment in both broth culture and food systems increased as the temperature was reduced(25C-5C) and as the pH decreased(pH6.5-pH5.5). Food system studies demonstrated that modified atmosphere packaging(96.58%N2 , 2.09%O2 and 1.34% CO2) has no influence of the growth of L. monocytogenes. The susceptibility of L. monocytogenes to lysozyme-GDL was a stable characteristic, remaining unchanged during the entire study. Attempts to select for greater lysozyme-GDL resistance by testing populations grown from lysozyme-GDL survivors isolated at the end of the food system study was unsuccessful. There was no evidence that L. monocytogenes was resistant to the lysozyme-GDL treatment.