Doctoral Degrees (Microbiology)

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Browsing Doctoral Degrees (Microbiology) by Author "Benade, Eliska"

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    Binary interactions between bacteria and Candida albicans
    (Stellenbosch : Stellenbosch University, 2017-03) Benade, Eliska; Botha, Alfred; Mouton, Marnel; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: The primary habitat of the ascomycetous yeast Candida albicans is thought to be the mammalian gastrointestinal (GI) tract. This opportunistic pathogen however, was also found to be capable of sustainable growth in the anaerobic zones of fecal contaminated rivers. Although it is known that bacteria may impact the survival of C. albicans under aerobic conditions, the effect of an anaerobic environment on these bacteria/yeast interactions has never been explored. Therefore, using both aerobic and anaerobic liquid co-cultures, binary interactions between C. albicans and a number of environmental bacterial isolates were studied at 26ºC. The bacteria represented Aeromonas hydrophila, Bacillus cereus, Bacillus subtilis, Clostridium, Enterobacter, Klebsiella pneumoniae, Kluyvera ascorbata and Serratia marcescens. Using plate counts it was found that bacterial growth inhibits the yeast’s growth under aerobic conditions; however, the inhibitory effect was ameliorated under anaerobic conditions. Bacterial enzymes capable of degrading yeast cell walls, including chitinases and mannanases, were produced by the majority of the bacteria. In contrast, except for A. hydrophila, these enzymes were not detected in anaerobic bacterial cultures, nor was the antimicrobial compound, prodigiosin found in anaerobic cultures of S. marcescens. Crude extracellular enzyme preparations from K. pneumoniae and S. marcescens had no effect on the yeast’s growth, but were found to enhance the toxicity of prodigiosin towards the yeast, especially in combination with mannanases. The above-mentioned in vitro methods were also used to study binary interactions at 37ºC between C. albicans and selected GI bacteria. The latter included Bacteroides fragilis, Bacteroides vulgatus, Clostridium perfringens, Escherichia coli, K. pneumoniae, Lactobacillus acidophilus and Lactobacillus plantarum. Using live/dead yeast viability staining in combination with epifluorescence microscopy it was demonstrated that the aerobic filamentous phase of C. albicans, which is usually induced at 37ºC, was either killed or inhibited by the bacteria; however, the bacteria had no effect on anaerobic yeast growth. Mannanase containing crude enzyme preparations from K. pneumoniae and B. fragilis also had no effect on anaerobically cultured yeast cells. Also, the enzyme preparations did not enhance the antagonistic effect of antimicrobials, such as Amphotericin B and prodigiosin, towards the yeast. Generally, bacterial growth was unaffected by the presence of C. albicans, neither at 26 or 37ºC, nor under aerobic or anaerobic conditions. Under anaerobic conditions at 37ºC however, the presence of either C. albicans or the model ascomycete Saccharomyces cerevisiae, significantly increased the numbers of mannan utilizing B. fragilis and B. vulgatus. Conversely, this increase was not as pronounced in the presence of engineered S. cerevisiae strains with compromised cell wall mannan layers. Treating monocultures of the two Bacteroides species with intact dead yeast cells also resulted in significant increases in bacterial numbers, while removal of the cell wall mannan layers from these dead yeasts resulted in no increase in Bacteroides numbers. These findings indicated that mannan utilizing Bacteroides strains may form commensalistic interactions with C. albicans. Overall, our findings suggest that the symbioses between C. albicans and bacteria may differ depending on the presence or absence of oxygen.