Transcriptional regulation of fluconazole susceptibility in Candida parapsilosis

Purpose: Candida parapsilosis is a major (yet understudied) cause of mucosal and invasive fungal infections in the United States. The development of high level azole resistance in C. parapsilosis has recently been reported in bloodstream isolates. The ability to develop resistance to this antifungal class during therapy or prophylaxis makes this a significant problem in the management of candidiasis.

Methods: Using a new genome-wide expression study technique (RNA-Seq) and real-time RT-PCR, we identified regulatory networks involved in azole resistance in C. parapsilosis. We compared the changes in gene expression between clinical matched fluconazole-susceptible and –resistant C. parapsilosis isolates representing the development of high-level azole antifungal resistance during a course of fluconazole therapy used to treat endocarditis (isolate set 35177 (MIC <1µg/ml) versus 35176 (MIC >64µg/ml)) and during routine use of fluconazole prophylaxis in a NICU (isolate set KC18 (MIC <2µg/ml) versus KC23 (MIC >64µg/ml)).

Results: Although these isolates have similar azole susceptibility patterns, the mechanisms of resistance appear to be different. The 35176 isolate had increased expression of genes encoding proteins involved in the ergosterol biosynthesis pathway, the target of the azole antifungals. The KC23 isolate had increased expression of genes encoding major facilitator transporter proteins which are known to efflux fluconazole out of the cell in other Candida species.

Conclusion: The contribution of this research is detailed understanding of the molecular pathways involved in azole resistance in C. parapsilosis and is expected to lead to development of pharmacologic strategies that will circumvent the problem of azole resistance in all Candida species. As these pathways are controlled by fungal specific transcriptional regulators in other Candida species, further studies are being conducted to elucidate the transcriptional control of these pathways in these C. parapsilosis clinical isolates.