The First Isolation of Multiple Antifungal-Drug-Resistant Trichophyton Rubrum in China and the Novel Resistance Mechanism.

OBJECTIVES

This study reports the first isolation of a multidrug-resistant Trichophyton rubrum strain in China, characterizing its drug resistance profile and mechanisms.

METHODS

The isolate was identified by internal transcribed spacer (ITS) sequencing and phylogenetic analysis. In vitro antifungal susceptibility testing (AFST) was performed according to the M38-A3 CLSI guideline to determine minimum inhibitory concentrations (MICs) against eight antifungals (terbinafine, itraconazole, fluconazole, amorolfine, griseofulvin, voriconazole, luliconazole and amphotericin B). Whole genome sequencing (WGS), transcriptome sequencing and qRT-PCR were performed to explore the resistance mechanism.

RESULTS

The multidrug-resistant T. rubrum strain L-6424 was isolated from a Chinese patient with generalised tinea corporis/cruris, tinea unguium and tinea manuum. It exhibited elevated MICs to terbinafine (2 mg/L), itraconazole (0.5 mg/L), and amorolfine (0.5 mg/L). The phylogenetic tree based on genome-wide single nucleotide polymorphisms (SNPs) showed L-6424 is not a novel genotype of T. rubrum, with high genetic similarity (99.94%) with the reference strain (CBS 139224). There were three amino acid substitutions in the squalene epoxidase (SQLE), including the previously reported F397L and H440Y, as well as a newly discovered V105M, and one amino acid substitution in the CYP51A (R239C) was identified. Also, significant differences at the transcriptome level between the drug-resistant and sensitive strains were observed, and it was screened and found that CYP51A, TruMDR5 and TERG_08139 may be related to azole resistance.

CONCLUSIONS

Drug-resistant T. rubrum has emerged in China, indicating the possibly increasing severity of antifungal resistance. The complex mechanism of multidrug-resistant dermophytes poses challenges to clinical treatment, needing more attention.