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

Abstract

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.

Keywords: Trichophyton rubrum; CYP51A; MDR5; SQLE; antifungal resistance; dermatophytosis; itraconazole; terbinafine.