Substrate Utilization of the Emerging Fungal Pathogen, Candida auris, and the Antifungal Activity of Select Essential Oils
Date of Award
Master of Science in Integrative Biology (MSIB)
First Committee Member
Second Committee Member
Third Committee Member
Candida auris is an emerging fungal pathogen that commonly causes nosocomial blood infections in the immunocompromised. Three factors make this emerging pathogen a global threat. First, it is frequently misidentified by commonly used diagnostic platforms. Second, it is able to survive for weeks on fomites. Third, it is almost always drug resistant, sometimes to all three classes of antifungal drugs used to treat Candida infections. The objectives of this study are three-fold. First, two existing methods, population estimation using absorbance-based standard curves and methylene blue viability staining, were investigated as to application in determining Candida auris cell population size and viability, respectively. Both the spectrophotometric study and methylene blue staining were successfully applied to C. auris concentrations. A standard curve plotting absorbance to concentration were constructed for several organisms for standardizing inoculum for subsequent assays. Second, a description of the basic metabolic capabilities of Candida auris to assimilate a variety of chemicals as a sole source of carbon or nitrogen was determined and compared to related yeasts. Candida auris displayed a unique pattern of carbon and nitrogen assimilation as compared to the other, related species. This included several carbon sources that may have future utility in a diagnostic media. Several isolates of C. auris were also examined using the Biolog YT plate for yeast identification, which operates under a similar principle. Although the organism is absent from database and thus misidentified as one of two organisms in all cases, a significant amount of carbon utilization data was added to the results of the previous study. Third, the antifungal activities of select essential oils were tested against C. auris. This was followed by testing the interaction of the three most effective oils with four commonly used antifungal drugs. Several of the essential oils displayed the ability to inhibit the growth or even kill C. auris, Candida lusitaniae, and Saccharomyces cerevisiae when in direct contact. The three most effective oils were those of lemongrass, clove bud and cinnamon bark. These three oils even retained some antifungal activity in vapor-phase. These were also the oils used in combination with fluconazole, amphotericin B, flucytosine and micafungin. While cinnamon bark oil displayed little interaction with the drugs, lemongrass oil displayed positive or neutral interactions with all four drugs, while clove bud oil had mixed results. The combination of clove bud oil and amphotericin B resulted in an antagonistic outcome, whereas it showed no improved effect when combined with micafungin but displayed positive interactions with fluconazole and flucytosine.