Trichophyton indotineae Erg1Ala448Thr Strain Expressed Constitutively High Levels of Sterol 14-α Demethylase Erg11B mRNA, While Transporter MDR3 and Erg11A mRNA Expression Was Induced After Addition of Short Chain Azoles.

Trichophyton indotineae is an emerging pathogen causing recalcitrant skin infections and exhibiting multiple resistances to azoles and allylamines. Squalene epoxidase erg1^Ala448Thr mutants often show association with azole resistance. RT-PCR gene expression analysis helps to elucidate the connection between ergosterol biosynthesis regulation and efflux control through the activation of multidrug resistance (MDR) and major facilitator superfamily (MFS1) transporters as well as heat shock proteins (HSP). Several T. indotineae isolates demonstrated a heat-dependent increase of Erg11B transcripts combined with downregulation of Erg1, suggesting a protective role for Erg11B. They also showed persistent upregulation of MFS1. The addition of fluconazole or voriconazole induced the expression of Erg11A, MDR3 and, to a lesser extent, Erg11B and Erg1. The azole-resistant erg1^Ala448Thr mutant UKJ 476/21 exhibited exceptionally high transcript levels of sterol 14-αdemethylase Erg11B, combined with the inability of HSP60 and HSP90 to respond to increasing growth temperatures. Itraconazole demonstrated similar effects in a few T. indotineae isolates, but terbinafine did not enhance Erg1 transcription at all. Overexpression of Erg11B may explain the multiple azole resistance phenotype, whereas Erg11B point mutations are not associated with resistance to azoles used for medical treatment.