Background: Candida albicans is an opportunistic human fungal pathogen and a causative agent of oropharyngeal candidiasis (OPC), the most frequent opportunistic infection among patients with AIDS. Fluconazole has proven effective in the management of OPC; however, with increased use of this agent, treatment failures have occurred. Such failures have been associated with the emergence of azole-resistant strains of C. albicans. In an effort to identify novel molecular mechanisms of azole resistance, we examined changes in the genome-wide gene expression profile of two series of serial C. albicans clinical isolates representing the acquisition of fluconazole resistance. Methods: Isolates were obtained from an AIDS patient with oropharyngeal candidiasis who failed fluconazole therapy (isolates F1, MIC=2 µg/mL; F3, MIC=4 µg/mL; F5, MIC=•64 µg/mL; G1, MIC=0.5; G3, MIC=8; and G5, MIC=16 µg/ml). Isolate F5 has previously been shown to exhibit increased expression of MDR1 and ERG11 as compared to isolate F1, whereas isolate G5 exhibits increased expression of MDR1 and loss of allelic variation in ERG11 as compared to isolate G1, in association with the acquisition of fluconazole resistance. Total RNA was isolated for DNA microarray analysis. Gene expression profiles were compared between isolates F1, F3 and F5 as well as G1, G3, and G5. Genes were considered to be differentially expressed if their average balanced differential expression ratio was •2 or •0.5. Experiments were performed in duplicate. Results: We found 11 genes to be up-regulated and 9 genes to be down-regulated in the F series of isolates, and 13 genes to be up-regulated and 1 gene to be down-regulated in the G series of isolates. In addition to MDR1, 10 genes (IFD1, IFD2, IFD4, IFD5, IFD7, GRP2, IPF17186, IPF5987, IPF1153, and IPF7940) were similarly differentially expressed in both series. Of these, all but IFD2 and IPF17186 were previously reported by us to be coordinately regulated with MDR1 in a separate matched series of azole-susceptible and -resistant isolates. Furthermore, 3 genes found to be differentially expressed in only one or the other of these series were previously reported by us to be differentially expressed in association with azole resistance (DDR48, ERG5, and YHB1). Conclusion: Many of these genes are involved in the oxidative stress response suggesting that reduced susceptibility to oxidative damage may contribute to azole resistance. These results implicate genes potentially involved in novel mechanisms of azole antifungal resistance and may lend insight into the mechanisms of their coordinate regulation. Further evaluation of the role of these genes and their respective gene products in this process is warranted.
Full conference title:
The 15 th Congress of the International Society for Human and Animal Mycology
- ISHAM 15th (2003)