Contribution of Clinically Derived Mutations in the Gene Encoding the Zinc Cluster Transcription Factor Mrr2 to Fluconazole Antifungal Resistance and Expression in .

Mutations in genes encoding zinc cluster transcription factors (ZCFs) such as , , and play a key role in azole antifungal resistance. Artificial activation of the ZCF Mrr2 has shown increased expression of the gene encoding the Cdr1 efflux pump and resistance to fluconazole. Amino acid substitutions in Mrr2 have recently been reported to contribute to fluconazole resistance in clinical isolates. In the present study, 57  clinical isolates with elevated fluconazole MICs were examined for mutations in and expression of Mutations in resulting in 15 amino acid substitutions were uniquely identified among resistant isolates, including 4 substitutions (S466L, A468G, S469T, T470N) previously reported to reduce fluconazole susceptibility. Three additional, novel amino acid substitutions (R45Q, A459T, V486M) were also discovered in fluconazole-resistant isolates. When introduced into a fluconazole-susceptible background, no change in fluconazole MIC or expression was observed for any of the mutations found in this collection. However, introduction of an allele leading to artificial activation of Mrr2 increased resistance to fluconazole as well as expression. Moreover, Mrr2 amino acid changes reported previously to have the strongest effect on fluconazole susceptibility and expression also exhibited no differences in fluconazole susceptibility or expression relative to the parent strain. While all known fluconazole resistance mechanisms are represented within this collection of clinical isolates and contribute to fluconazole resistance to different extents, mutations in do not appear to alter expression or contribute to resistance in any of these isolates.