Candida parapsilosis Mdr1B and Cdr1B Are Drivers of Mrr1-Mediated Clinical Fluconazole Resistance.

Candida parapsilosis is a common cause of invasive candidiasis worldwide and is the most commonly is7olated species among pediatric and neonatal populations. Previous work has demonstrated that nonsynonymous mutations in the gene encoding the putative transcription factor CpMrr1 can influence fluconazole susceptibility. However, the direct contribution of these mutations and how they influence fluconazole resistance in clinical isolates are poorly understood. We identified 7 nonsynonymous mutations in 12 isolates from within a collection of 35 fluconazole-resistant clinical isolates. The mutations leading to the A854V, R479K, and I283R substitutions were further examined and found to be activating mutations leading to increased fluconazole resistance. In addition to , we identified two other genes, one encoding a major facilitator superfamily (MFS) transporter (, CPAR2_603010) and one encoding an ATP-binding cassette (ABC) transporter (, CPAR2_304370), as being upregulated in isolates carrying -activating mutations. Overexpression of in a susceptible strain and disruption in resistant clinical isolates that overexpress had little to no effect on fluconazole susceptibility. Conversely, overexpression of either or increased resistance, and disruption in clinical isolates overexpressing these genes decreased fluconazole resistance. Our findings suggest that activating mutations in represent important genetic determinants of fluconazole resistance in clinical isolates of C. parapsilosis, and unlike what is observed in Candida albicans, this is primarily driven by upregulation of both MFS (CpMdr1B) and ABC (CpCdr1B) transporters.