A Study on the Species Diversity, Mating Types, and Clinical Relevance of Trichophyton mentagrophytes/interdigitale Complex Infections in Guizhou Province

To date, no reliable biological clock markers have been identified to elucidate the phylogenetic relationships among the three species within the Trichophyton mentagrophytes complex-namely T. interdigitale, T. mentagrophytes, and T. indotineae. This study, employing a polyphasic approach, confirmed that 62 clinical isolates of the T. mentagrophytes complex obtained from Guizhou tend to cluster into two distinct groups: Group I (42 isolates, comprising T. interdigitale and T. indotineae) and Group II (20 isolates, representing T. mentagrophytes). These groups exhibited statistically significant differences in molecular characteristics, phenotypic traits, MAT locus distribution, clinical pathogenicity, and antifungal susceptibility profiles. Notably, the identification of a cryptic sexual state in T. interdigitale revealed unexpected genetic affinities between the two groups. In particular, the hybrid strain JYP 23487, classified as T. mentagrophytes, and its granular variant JYP 23487 k, which occupies an intermediate position in the MAT1-1 gene phylogenetic tree (MAT1-1-1 genotype C), provide evidence for genetic continuity and suggest a potential link between fungal morphological variation and mating type gene composition. Collectively, the Guizhou isolates of the T. mentagrophytes complex demonstrate a dynamic pattern of genetic continuity and shared MAT genotypes that correlate with phenotypic traits, providing additional evidence for the blurred taxonomic boundaries between the traditionally defined species T. interdigitale and T. mentagrophytes. The occurrence of strains with dual mating type loci or intermediate genotypes may be attributed to frequent host switching, facilitating recombination and exchange of MAT gene regions.