Defining the relationship between phylogeny, clinical manifestation and phenotype for Trichophyton mentagrophytes/interdigitale complex; a literature review and taxonomic recommendations.

This study looked for correlations between molecular identification, clinical manifestation and morphology for Trichophyton interdigitale and T. mentagrophytes. For this purpose, a total of 110 isolates were obtained from Czech patients with various clinical manifestations of dermatophytosis. Phenotypic characters were analysed, and the strains were characterized using multilocus sequence typing. Among the 12 measured/scored phenotypic features, statistically significant differences between species were found only in growth rates at 37°C and in the production of spiral hyphae. Correlations were found between T. interdigitale and higher age of patients and between clinical manifestations such as tinea pedis or onychomychosis. In addition, the T. interdigitale lineage consisted exclusively of isolates with MAT1-2-1 mating type gene idiomorphs. The MLST approach showed that ITS genotyping of T. mentagrophytes isolates has limited practical benefits because of extensive gene flow between sublineages. Based on our results and previous studies, there are few taxonomic arguments for preserving both species names. The species show a lack of monophyly and unique morphology. On the other hand, some genotypes are associated with predominant clinical manifestations and sources of infections, which keep those names alive. This practice is questionable because the use of both names confuses identification, leading to difficulty in comparing epidemiological studies. The current identification method using ITS genotyping is ambiguous for some isolates and is not user-friendly. Additionally, identification tools such as MALDI-TOF MS fail to distinguish these species. To avoid further confusion and simplify identification in practice, we recommend using the name T. mentagrophytes for the entire complex. When clear differentiation of populations corresponding to T. interdigitale and T. indotineae is possible based on molecular data, we recommend optionally using a variety rank: T. mentagrophytes var. interdigitale and T. mentagrophytes var. indotineae.