Species Distinction in the Trichophyton mentagrophytes Complex Based on Phylogenomic Analysis.

Objective: Trichophyton mentagrophytes complex species mainly cause superficial infections, with a high global incidence and affecting the quality of life of patients. The taxonomic identification between closely related species within the T. mentagrophytes complex remains problematic, especially between T. mentagrophytes and T. interdigitale. This study aimed to elucidate the species boundaries within the T. mentagrophytes complex.

Methods: We performed a phylogenetic tree, principal component analysis and population structure analysis based on whole genome single-nucleotide polymorphism (SNP) data of 157 T. mentagrophytes complex strains. The mating types, phenotypic and physiological characteristics of different populations of strains were detected to delimit the species within the complex.

Results: The phylogenomic analysis showed that the 157 T. mentagrophytes complex strains were divided into five populations and clustered into three major clades, namely the T. tonsurans (population I), T. interdigitale (populations II, III and V) and T. mentagrophytes (population IV) clades. T. interdigitale population III was significantly different from T. interdigitale population II in terms of nucleotide diversity, mating types, types of clinical disease caused and keratinolytic ability but similar to those of T. mentagrophytes population IV.

Conclusions: T. tonsurans, T. interdigitale and T. mentagrophytes could be regarded as independent species and all strains were divided into five populations. The finding that T. interdigitale population III strains (T. mentagrophytes genotype Tm-II*) are reclassified as T. interdigitale based on whole-genome analysis is notable and clarifies previous confusion in clinical microbiology labs.