Fluconazole and Voriconazole Resistance in Candida parapsilosis Is Conferred by Gain-of-Function Mutations in MRR1 Transcription Factor Gene

Abstract

e Candida parapsilosis is the second most prevalent fungal agent causing bloodstream infections. Nevertheless, there is little information about the molecular mechanisms underlying azole resistance in this species. Mutations (G1747A, A2619C, and A3191C) in the MRR1 transcription factor gene were identified in fluconazole-and voriconazole-resistant strains. Independent expression of MRR1 genes harboring these mutations showed that G1747A (G583R) and A2619C (K873N) are gain-of-function mutations responsible for azole resistance, the first described in C. parapsilosis.

Fluconazole‐resistant Candida parapsilosis strains with a Y132F substitution in the ERG11 gene causing invasive infections in a neonatal unit, South Africa

“…Initial studies indicate these substitutions change fluconazole susceptibility in C parapsilosis isolates as they were identified exclusively in SDD and resistant isolates 13,26 . Branco et al (2015) successfully demonstrated that G583R confers hyperactivity to MRR1 transcription factor leading to upregulation of MDR1 drug transporter 16 . In the present study, A619V was found in 2 SDD and 4 resistant isolates.…”

“…Resistance may occur in one of the following ways: (a) point mutations in ERG11 gene, resulting in reduced azole binding affinity; (b) overexpression of the drug target ( ERG11 ) gene which encodes for 14α demethylase; (c) overexpression of the genes encoding multidrug transporters [ATP binding cassettes (ABC) and major facilitator superfamily (MFS)]; (d) overexpression of CDR1 and CDR caused by activating mutations in the transcription factor genes TAC1 leading to efflux of all azole antifungal agents 8 ; (e) overexpression of an MFS transporter ( MDR1 ) caused by activating mutations in the transcription factor genes MRR1 leading to efflux of fluconazole and voriconazole 9‐11 ; and (f) mutations in ERG3 gene resulting in the inactivation of sterol desaturase. A number of studies from the United States of America, United Kingdom, Brazil, Portugal, South Korea and India have recently explored the possible mechanisms of azole resistance in C parapsilosis strains 12‐17 . Souza et al (2015) demonstrated that not only does upregulation of MDR1 and amino acid substitutions in ERG11 lead to resistance to fluconazole but upregulation of ERG11 and CDR1 are involved as well 14 .…”

Azole Antifungal Resistance in Candida albicans and Emerging Non-albicans Candida Species

“…In a study using laboratory strains of C. parapsilosis in which previously-determined gain-of-function alleles of CpMRR1 were introduced into the native locus, strains containing Mrr1p with a G583R amino acid substitution from a fluconazole-resistant C. parapsilosis isolate led to resistant fluconazole and voriconazole MIC compared to strains harboring the wildtype allele (Branco et al, 2015). Similarly, strains with single SNP-containing MRR1 alleles had a ~5-fold increase in MRR1 gene expression and ~70-fold increase in MDR1 gene expression.…”

Competitive Fitness of Fluconazole-Resistant Clinical Candida albicans Strains

“…In addition, cocultures were started with 3.7 ϫ 10 6 cells/ml in the study by Lohberger et al (8), which amounts to only ca. 7 generations until stationary phase is reached, whereas the cocultures were grown for FIG 5 Competitive fitness of fluconazole-susceptible isolates F2, B3, 5833, and TW1 (light gray bars) and matched fluconazoleresistant isolates F5, B4, 6692, and TW17 (dark gray bars), respectively, in a mouse model of disseminated candidiasis. In each case, the susceptible isolate was mixed with two independently generated RFP-labeled derivatives of the matched resistant isolate and the resistant isolate was mixed with two independently generated RFP-labeled derivatives of the matched susceptible isolate.…”

“…The most commonly observed resistance mechanisms are mutations in the drug target enzyme Erg11, which reduce drug binding, and gain-of-function (GOF) mutations in the zinc cluster transcription factors (ZnTFs) Mrr1, Tac1, and Upc2, which result in changes in gene expression that promote drug resistance (2-4). Specifically, GOF mutations in Mrr1 cause overexpression of the multidrug efflux pump MDR1 and additional genes that contribute to fluconazole resistance (5)(6)(7)(8)(9)(10)(11). Similarly, GOF mutations in Tac1 confer fluconazole resistance by mediating overexpression of the multidrug efflux pumps CDR1 and CDR2 and other Tac1 target genes (12)(13)(14)(15)(16)(17).…”