Binary interactions between bacteria and Candida albicans

[摘要] ENGLISH ABSTRACT: The primary habitat of the ascomycetous yeast Candida albicans is thought to be themammalian gastrointestinal (GI) tract. This opportunistic pathogen however, was also foundto 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 aerobicconditions, the effect of an anaerobic environment on these bacteria/yeast interactions hasnever been explored. Therefore, using both aerobic and anaerobic liquid co-cultures, binaryinteractions between C. albicans and a number of environmental bacterial isolates werestudied at 26ºC. The bacteria represented Aeromonas hydrophila, Bacillus cereus, Bacillussubtilis, Clostridium, Enterobacter, Klebsiella pneumoniae, Kluyvera ascorbata and Serratiamarcescens. Using plate counts it was found that bacterial growth inhibits the yeast's growthunder aerobic conditions; however, the inhibitory effect was ameliorated under anaerobicconditions. Bacterial enzymes capable of degrading yeast cell walls, including chitinases andmannanases, 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 theantimicrobial compound, prodigiosin found in anaerobic cultures of S. marcescens. Crudeextracellular enzyme preparations from K. pneumoniae and S. marcescens had no effect onthe 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 37ºCbetween 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 viabilitystaining in combination with epifluorescence microscopy it was demonstrated that the aerobicfilamentous phase of C. albicans, which is usually induced at 37ºC, was either killed orinhibited by the bacteria; however, the bacteria had no effect on anaerobic yeast growth.Mannanase containing crude enzyme preparations from K. pneumoniae and B. fragilis alsohad no effect on anaerobically cultured yeast cells. Also, the enzyme preparations did notenhance 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 or37ºC, nor under aerobic or anaerobic conditions. Under anaerobic conditions at 37ºChowever, the presence of either C. albicans or the model ascomycete Saccharomycescerevisiae, 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 thetwo Bacteroides species with intact dead yeast cells also resulted in significant increases inbacterial numbers, while removal of the cell wall mannan layers from these dead yeastsresulted in no increase in Bacteroides numbers. These findings indicated that mannanutilizing Bacteroides strains may form commensalistic interactions with C. albicans. Overall,our findings suggest that the symbioses between C. albicans and bacteria may differdepending on the presence or absence of oxygen.

[发布机构] Stellenbosch University