Mutations in TAC1B drive increased CDR1 and MDR1 expression and azole resistance in Candida auris.

Candida auris has emerged as a fungal pathogen of particular concern owing in part to its propensity to exhibit antifungal resistance, especially to the commonly prescribed antifungal fluconazole. A mutation in TAC1B, which encodes a zinc cluster transcription factor, has been shown to confer increased resistance to fluconazole. In this work, we aimed to determine how mutations in TAC1B exert this effect. TAC1B mutations leading to A640V, A657V, and F862_N866del, found in fluconazole-resistant clinical isolates, were introduced into two susceptible Clade I backgrounds using CRISPR-Cas9 gene editing. These TAC1B mutations conferred increased fluconazole resistance, as well as increased resistance to other triazoles as measured by broth microdilution. RNA-seq revealed that the ATP-binding cassette (ABC) transporter gene CDR1 as well as the major facilitator superfamily (MFS) transporter gene MDR1 were both upregulated in the presence of these TAC1B mutations. Disruption of CDR1 increased susceptibility in strains with TAC1B mutations, whereas disruption of MDR1 had little to no effect. However, disruption of both CDR1 and MDR1 resulted in an additional increase in susceptibility as compared with disruption of CDR1 alone. TAC1B mutations, leading to A640V, A657V, and F862_N866del all result in increased resistance to fluconazole and other triazole antifungals and increased expression of both CDR1 and MDR1 in C. auris. Together, these data suggest CDR1 is the primary driver of resistance conferred by these TAC1B mutations.