title: Azole resistance by loss of function of the sterol Δ⁵,⁶-desaturase gene (ERG3) in Candida albicans does not necessarily decrease virulence.
abstract: The inactivation of ERG3, a gene encoding sterol Δ⁵,⁶-desaturase (essential for ergosterol biosynthesis), is a known mechanism of in vitro resistance to azole antifungal drugs in the human pathogen Candida albicans. ERG3 inactivation typically results in loss of filamentation and attenuated virulence in animal models of disseminated candidiasis. In this work, we identified a C. albicans clinical isolate (VSY2) with high-level resistance to azole drugs in vitro and an absence of ergosterol but normal filamentation. Sequencing of ERG3 in VSY2 revealed a double base deletion leading to a premature stop codon and thus a nonfunctional enzyme. The reversion of the double base deletion in the mutant allele (erg3-1) restored ergosterol biosynthesis and full fluconazole susceptibility in VSY2, confirming that ERG3 inactivation was the mechanism of azole resistance. Additionally, the replacement of both ERG3 alleles by erg3-1 in the wild-type strain SC5314 led to the absence of ergosterol and to fluconazole resistance without affecting filamentation. In a mouse model of disseminated candidiasis, the clinical ERG3 mutant VSY2 produced kidney fungal burdens and mouse survival comparable to those obtained with the wild-type control. Interestingly, while VSY2 was resistant to fluconazole both in vitro and in vivo, the ERG3-derived mutant of SC5314 was resistant only in vitro and was less virulent than the wild type. This suggests that VSY2 compensated for the in vivo fitness defect of ERG3 inactivation by a still unknown mechanism(s). Taken together, our results provide evidence that contrary to previous reports inactivation of ERG3 does not necessarily affect filamentation and virulence.
authors.affiliation: Institute of Microbiology, University of Lausanne and University Hospital Center, Lausanne, Switzerland.
authors.forename: L A
authors.initials: LA
authors.lastname: Vale-Silva
authors.forename: A T
authors.initials: AT
authors.lastname: Coste
authors.forename: F
authors.initials: F
authors.lastname: Ischer
authors.forename: J E
authors.initials: JE
authors.lastname: Parker
authors.forename: S L
authors.initials: SL
authors.lastname: Kelly
authors.forename: E
authors.initials: E
authors.lastname: Pinto
authors.forename: D
authors.initials: D
authors.lastname: Sanglard
mesh_terms: D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology*; D001393:Azoles / Q000494:pharmacology*; D018441:Biofilms; D015152:Blotting, Northern; D015139:Blotting, Southern; D002176:Candida albicans / Q000201:enzymology* / Q000235:genetics* / Q000472:pathogenicity; D002177:Candidiasis / Q000188:drug therapy / Q000382:microbiology; D004271:DNA, Fungal / Q000235:genetics; D025141:Drug Resistance, Fungal / Q000235:genetics*; D005260:Female; D015725:Fluconazole / Q000494:pharmacology / Q000627:therapeutic use; D005456:Fluorescent Dyes; D008401:Gas Chromatography-Mass Spectrometry; D007668:Kidney / Q000382:microbiology / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D012235:Rhodamines; D014774:Virulence
chemical_list: D000935:Antifungal Agents; D001393:Azoles; D004271:DNA, Fungal; D005456:Fluorescent Dyes; D012235:Rhodamines; C026188:rhodamine 6G; D015725:Fluconazole; D010088:Oxidoreductases; C039306:sterol delta-5 desaturase