Gene Amplification of CYP518: a New Mechanism of Resistance to Azole Compounds in Trichophyton indotineae

Trichophyton indotineae causes dermatophytosis that is resistant to terbinafine and azole compounds. The aim of this study was to determine the mechanisms of resistance to itraconazole (ITC) and voriconazole (VRC) in strains of T. indotineae. Two azole-sensitive strains (ITC MIC < 0.125 mu g/mL; VRC MIC < 0.06 mu g/mL) and four azole-resistant strains (ITC MIC >= 0.5 mu g/mL; VRC MIC >= 05 mu g/mL) were used for the investigation. The expression of MDR genes encoding multidrug transporters of the ABC family for which orthologs have been identified in Trichophyton rubrum and those of CYP51A and CYP518 encoding the targets of azole antifungal compounds were compared between susceptible and resistant strains. TinMDR3 and TinCYP518 were overexpressed in T. indotineae resistant strains. Only small differences in susceptibility were observed between TinMDR3 disruptants and parental strains overexpressing TinMDR3. Whole-genome sequencing of resistant strains revealed the creation of a variable number of TinCYP518 tandem repeats at the specific position of their genomes in three resistant strains. Downregulation of TinCYP518 by RNA interference (RNAi) restored the susceptibility of azole-resistant strains. In contrast, overexpression of TinCYP518 cDNA conferred resistance to a susceptible strain of T. indotineae. In conclusion, the reduced sensitivity of T. indotineae strains to azoles is mainly due to the overexpression of TinCYP518 resulting from additional copies of this gene.