Genomic insights into the dermatophyte Trichophyton indotineae in Singapore: Resistance and transmission dynamics

During an 11-month study at two hospital sites, 33 isolates initially classified as the Trichophyton mentagrophytes complex were subjected to whole-genome sequencing. Of these, 24 (72.7%) were identified as T. indotineae and 9 (27.3%) as T. interdigitale, with no T. mentagrophytes detected. Among the 22 patients with available clinical data, 75% exhibited involvement of multiple anatomical sites; although only two patients reported recent travel, 63.6% were migrant workers. Symptom resolution was documented in only four patients, whereas five experienced recurrences. Nearly 80% of T. indotineae isolates displayed terbinafine resistance linked to squalene epoxidase mutations, while no phenotypic azole resistance was observed, consistent with the absence of cyp51 mutations. Single-nucleotide polymorphism (SNP) analysis of both T. indotineae (520-1531 SNPs) and T. interdigitale (1380-115 963 SNPs) revealed no phylogenetic clustering, suggesting independent introductions.