Tandem of sequences encoding CYP51B in Trichophyton indotineae.

Trichophyton indotineae is an emerging dermatophyte that causes severe tinea corporis and tinea cruris. Numerous cases of terbinafine- and azole-recalcitrant dermatophytosis due to this species have been observed in India over the past decade and cases are now being recorded worldwide. Whole genome sequencing of three azole-resistant strains revealed a variable number of repeats of a 2404-bp sequence encoding TinCYP51B in tandem at the specific position the CYP51B locus. However, many resistant strains did not contain such duplications. Whole-genome sequencing of three of these strains revealed a variable number of 7373-base-pair tandem repeat blocks harboring TinCYP51B. Consequently, two types of T. indotineae strains with low susceptibility to azoles host TinCYP51B in tandem sequences (type I with 2404 bp TinCYP51B blocks, type II with 7373 bp TinCYP51B blocks). Using the CRISPR/Cas9 genome editing tool, the copy number of TinCYP51B within the genome of type I and type II strains was brought back to a single copy. The azole resistance of these modified strains was similar to that of strains without CYP51B duplications, confirming that that the reduced sensitivity of T. indotineae strains to azoles is mediated by the amplification of the TinCYP51B gene.