Elucidation of Mechanism of Azole Resistance  of Multi-drug-resistant Trichophyton isolates

Tinea is assumed to affect 20% of the Japanese population and its main causative agents are Trichophyton rubrum, T. interdigitale, T. mentagrophytes, and etc. Terbinafine which is the allylamine antifungal drug has been used worldwide as the first-line drug for these infections. However, reports on TRF-resistant Trichophyton spp. have increased since 2017 and treatment for TRF-resistant strains has switched to giving azoles such as itraconazole (ITCZ) and voriconazole (VRCZ). Unfortunately, there are now a growing number of reports on multidrug-resistant Trichophyton spp. that are resistant to both TRF and azoles. Among TRF-resistant strains of IFM collection, one azole resistance of T. rubrum and three azole resistance of T. mentagrophytes were found. Especially, there were no reports of azole resistance in T. mentagrophytes, its mechanism of resistance remains unclear. Drug susceptibility tests of these strains revealed that these strains exhibited 8-32 times lower susceptibility to ITCZ and VRCZ compared to susceptible strains. In other pathogenic fungi, it has been reported that the mechanisms of azole resistance include amino acid mutation and/or overexpression of the Cyp51 gene encoding the target enzyme of azoles, and overexpression of the gene encoding the ATP-binding cassette (ABC) transporter. Therefore, the expression level of putative ABC transporter genes (MDR), Cyp51A and Cyp51B genes in resistant strains were compared with those of sesceptible strains. The result showed that MDR3 and Cyp51B were overexpressed in resistant strains of T. mentagrophytes. Now, we plan to conduct genetic recombination experiments to investigate whether such gene overexpression contributes to azole resistance.