A Zinc Cluster Transcription Factor Contributes to the Intrinsic Fluconazole Resistance of Candida auris

Abstract

The recently emerged pathogenic yeast Candida auris is a major concern for human health, because it is easily transmissible, difficult to eradicate from hospitals, and highly drug resistant. Most C. auris isolates are resistant to the widely used antifungal drug fluconazole due to mutations in the target enzyme Erg11 and high activity of efflux pumps, such as Cdr1. In the well-studied, distantly related yeast Candida albicans, overexpression of drug efflux pumps also is a major mechanism of acquired fluconazole resistance and caused by gain-of-function mutations in the zinc cluster transcription factors Mrr1 and Tac1. In this study, we investigated a possible involvement of related transcription factors in efflux pump expression and fluconazole resistance of C. auris. The C. auris genome contains three genes encoding Mrr1 homologs and two genes encoding Tac1 homologs, and we generated deletion mutants lacking these genes in two fluconazole-resistant strains from clade III and clade IV. Deletion of TAC1b decreased the resistance to fluconazole and voriconazole in both strain backgrounds, demonstrating that the encoded transcription factor contributes to azole resistance in C. auris strains from different clades. CDR1 expression was not or only minimally affected in the mutants, indicating that Tac1b can confer increased azole resistance by a CDR1-independent mechanism. IMPORTANCE Candida auris is a recently emerged pathogenic yeast that within a few years after its initial description has spread all over the globe. C. auris is a major concern for human health, because it can cause life-threatening systemic infections, is easily transmissible, and is difficult to eradicate from hospital environments. Furthermore, C. auris is highly drug resistant, especially against the widely used antifungal drug fluconazole. Mutations in the drug target and high activity of efflux pumps are associated with azole resistance, but it is not known how drug resistance genes are regulated in C. auris. We have investigated the potential role of several candidate transcriptional regulators in the intrinsic fluconazole resistance of C. auris and identified a transcription factor that contributes to the high resistance to fluconazole and voriconazole of two C. auris strains from different genetic clades, thereby providing insight into the molecular basis of drug resistance of this medically important yeast.

Genome-Wide Analysis of Experimentally Evolved Candida auris Reveals Multiple Novel Mechanisms of Multidrug Resistance

“…Based on these reports and our findings, we therefore hypothesize that F191Δ is a new potential gain of function mutation of C. auris TAC1b , conferring azole resistance through CDR1 overexpression. Nevertheless, previous reports have shown that Tac1b might function in other, Cdr1-independent ways to decrease azole susceptibility in C. auris ( 16 , 26 ). Another genetic adaptation linked to reduced azole susceptibility in this study involves aneuploidies.…”

“…2 ). Tac1b is a transcription factor that positively regulates the expression of the ATP binding cassette (ABC) transporter Cdr1, known to be involved in azole efflux and azole resistance in C. auris ( 16 , 26 ). Gene expression analysis of strain F12 (no TAC1b mutation) and strain F13 ( TAC1b mutation obtained) confirms that the acquisition of this mutation corresponds to a significantly increased expression of CDR1 (B9J08_000164), as shown in Fig.…”

“…Overall, few studies have actually been able to validate the proposed drug resistance mechanisms in C. auris ( 16 , 18 , 26 , 27 ), presumably because of the lack of an optimized gene-editing system. Here, we apply a strategy of serial transfer-based experimental evolution with the ability to trace back the emergence—and validate the cumulative effect—of single mutations or copy number changes throughout the evolutionary process.…”

Insights into the Multi-Azole Resistance Profile in Candida haemulonii Species Complex

“…Our recently published work demonstrated primary evidence that impariment of the mitochondrial function in C. haemulonii species complex intensifies the tolerance to stress and could be related with a rearrangement in the cellular ergosterol content [ 21 ]. In this context, growing evidence from recent elegant reports has revealed that there are more complicated and unknown drug resistance mechanisms apart from the mutational modification of the azole target ERG11p in fungal pathogens [ 59 , 60 , 61 , 62 ].…”

Chromatin Structure and Drug Resistance in Candida spp.

“…For the most part, the molecular bases of intrinsic resistance in Candida spp. are unknown [ 19 , 20 ], although recent research suggests that in C. auris at least, transcriptional regulation is key [ 21 ].…”