Development of Resistance to Antifungal Agents in Common Yeast Species
Date
2018Metadata
[+] Show full item recordAbstract
Pathogenic fungi are responsible for several serious diseases in both plants and animals with severe consequences in both medicine and agriculture. This makes treatment of fungal infections a prime concern for both economic and humanitarian concerns. Treatment for pathogenic fungus infections is hindered by the lack of development of new drugs that inhibit growth of fungi, as well as the mechanisms by which fungi develop resistance to existing drugs.
The development of new antifungal drugs is slow and requires a great deal of testing to ensure the drug is both safe and effective. It is therefore important that current drugs are used in a manner to prevent the development of resistance phenotypes. The growing number of pathogenic yeast infections has resulted in the greater use of antifungal drugs in patient treatment. With this increase in use, several strains have arisen with resistance to commonly used antifungal agents such as azoles and polyenes. Therefore, the characterization and study of mechanisms of drug resistance is of the utmost concern. The purpose of this study was to characterize how several species respond to drug challenge as well as the mechanisms guiding their responses.
ABC transporters are known for increasing drug resistance phenotype through increased efflux of drugs from the cell. In this thesis, two studies have been performed to examine the ways in which the expression of ABC transporters may lead to drug resistance. First, a commercially-available Saccharomyces cerevisiae strain exhibiting an azole resistance phenotype was determined to possess an overexpression of PDR5. Subsequently that strain was deleted of the efflux pump PDR5 and examined for the loss of the azole resistance phenotype. The resulting deletion strain exhibited a decrease in all drugs but retained some resistance to fluconazole and ketoconazole. Second, several putative ABC efflux transporters from Aspergillus fumigatus (AF) were heterologously expressed in a hyper-susceptible S. cerevisiae strain. The resulting strains exhibited differences in substrate specificity efflux that may shape the treatment of AF strains that express these transporters. Third, the further study of pathogenic yeasts was facilitated by the development of a table of Minimum Inhibitory Concentration (MIC) values for several common species against a variety of drugs and media. This table was created with the intent of provide basal MIC values in response to common environmental conditions to reduce time needed to establish testing conditions and basic growth conditions for the listed species.
Table of Contents
The role of PDR5 in the development of SC0000AZOLE resistance -- Characterization of putative aspergillus fumigatus ABC efflux transporters in hyper-susceptible s. cerevisiae strains -- Production of mic table for common laboratory yeast species -- Conclusion and future steps
Degree
M.S. (Master of Science)