Azole Resistance Mechanisms in Pathogenic Malassezia furfur

Malassezia spp. are emerging fungal pathogens causing opportunistic skin and severe systemic infection. Nosocomial outbreaks are associated with azole resistance, and understanding of the underlying mechanisms is limited to knowledge of other fungal species. Here, we identified distinct antifungal susceptibility patterns in 26 Malassezia furfur isolates derived from healthy and diseased individuals. A Y67F CYP51 mutation was identified in five isolates of M. furfur. However, this mutation alone was insufficient to induce reductions in azole susceptibility in the wild-type strain. RNA sequencing (RNA-seq) and differential gene analysis of strains derived from individuals with healthy or disease backgrounds exposed to clotrimazole in vitro identified several key metabolic pathways and transporter proteins which are involved in reducing azole susceptibility. The pleiotropic drug transporter gene PDR10 was the single most highly upregulated transporter gene in multiple strains of M. furfur after azole treatment, and increased expression of PDR10 is associated with reduced azole susceptibility in some systemic-disease isolates of M. furfur. Deletion of PDR10 in a pathogenic M. furfur strain with reduced susceptibility reduced MICs to those of susceptible isolates. In light of the current dearth of antifungal technologies, globally emerging multiazole resistance, and broad use of azoles in agriculture and consumer care, an improved understanding of the mechanisms underlying intrinsic and acquired azole resistance in Malassezia is crucial for development of antibiotic stewardship and antifungal treatment strategies.