Antifungal resistance of the Trichophyton mentagrophytes/Trichophyton interdigitale species complex: Insights from the China Antifungal Resistance Dermatophytes Surveillance network Study (CARDS)

BACKGROUND: Dermatophytosis caused by the Trichophyton mentagrophytes/T. interdigitale species complex (TMTISC) has attracted global attention, with increasing reports of terbinafine-resistant T. indotineae in China. OBJECTIVES: This study aims to evaluate the epidemiological features of antifungal-resistant TMTISC in China and monitor the prevalence of T. indotineae. METHODS: A total of 230 TMTISC strains were isolated from nine tertiary hospitals across three economic regions of China. These isolates were identified through molecular sequencing and phylogenetic analysis. Additionally, in vitro antifungal susceptibility testing (AFST) was performed for eight drugs, following the EUCAST 11.0 protocol. Mutations in the squalene epoxidase (SQLE) gene were detected. RESULTS: The phylogenetic tree revealed that 120 strains (52.17%) were T. mentagrophytes, 92 (40.0%) were T. interdigitale, and 18 (7.83%) were T. indotineae. Eight different genotypes were identified, including TM-IX, which was predominant in China, along with two newly discovered genotypes, TM-XXX and TM-XXXI. Among T. mentagrophytes isolates, tinea faciei (44.17%) was the common clinical type, primarily isolated from the central region. T. interdigitale isolates were mainly found in onychomycosis (36.96%), T. indotineae was commonly isolated from tinea corporis (94.44%) and tinea cruris (55.56%). AFST showed that all isolates of T. interdigitale and T. mentagrophytes were susceptible to terbinafine [minimum inhibitory concentrations (MICs) < 0.125 mg/L] and voriconazole (MICs < 0.5 mg/L). All isolates of T. indotineae were resistant to terbinafine (0.25 to >4.0 mg/L), exhibiting a single amino acid substitution in SQLE (Phe397Leu, Leu393Ser or Phe415Cys). Additionally, elevated MICs were observed in TMTISC for itraconazole, miconazole, ciclopirox (1-2 mg/L) and griseofulvin (1-64 mg/L). CONCLUSIONS: The TMTISC was predominantly composed of T. mentagrophytes, followed by T. interdigitale and T. indotineae. A rising trend of reduced azoles susceptibility in TMTISC and multi-drug resistance among T. indotineae isolates has been observed in China.