Species boundaries in the Trichophyton mentagrophytes / T. interdigitale species complex

Abstract

The fungi Trichophyton mentagrophytes and T. interdigitale are closely related species, causing superficial infections in humans and other mammals. The status of these taxa is a field of long-lasting debates. To clarify their phylogenetic relationships within the genus Trichophyton and sharpen the species boundaries, we performed sequencing of four T. mentagrophytes genomes and also evaluated three previously published multilocus data sets. We performed computational species delimitation analysis on all available in GenBank internal transcribed spacer region (ITS) sequences of Trichophyton spp. Phylogenomic data, phylogenetic network, and species delimitation analyses implied that T. mentagrophytes and T. interdigitale belong to the same phylogenetic species. However, we argue that taxonomic status quo should be retained, from the perspective of epidemiological data and the principle of taxonomic stability. Since there is a correlation between ITS genotype and epidemiological source of an isolate, restriction of T. interdigitale to purely anthropophilic ITS genotypes seems to be reasonable.

Trichophyton mentagrophytes and T interdigitale genotypes are associated with particular geographic areas and clinical manifestations

“…The remaining sequences were cropped. On the next step, the sequences which have been deposited in the database at least three times by laboratories from at least two countries were selected for statistical analysis and describing geographic distribution of genotypes (3/2 rule) …”

“…Therefore, molecular strain typing and species identification can be performed by the same DNA sequences. Differences in epidemiological sources and clinical pictures between particular genotypes provide the basis for species delineation . In the current classification, the name T interdigitale is reserved for exclusively anthropophilic isolates, mainly found in tinea unguium and tinea pedis cases, as opposed to zoophilic T mentagrophytes isolates, which also can be found in clinical cases other than nail and foot infections .…”

“…The species Trichophyton mentagrophytes and its clonal offshoot T interdigitale are exceptional among other Trichophyton species in having significant number of internal transcribed spacer (ITS) region genotypes and taken together account for 34% of genus' diversity. 1 Therefore, molecular strain typing and species identification can be performed by the same DNA sequences. Differences in epidemiological sources and clinical pictures between particular genotypes provide the basis for species delineation.…”

“…Differences in epidemiological sources and clinical pictures between particular genotypes provide the basis for species delineation. 1,2 In the current classification, the name T interdigitale is reserved for exclusively anthropophilic isolates, mainly found in tinea unguium and tinea pedis cases, as opposed to zoophilic T mentagrophytes isolates, which also can be found in clinical cases other than nail and foot infections. 3 For example, in the study of Heidemann and others, T interdigitale isolates (ITS Types I and II) were the causative agents of tinea unguium and tinea pedis in 93% cases, whereas T mentagrophytes strains were predominantly isolated from human tinea corporis and animal dermatophytosis.…”

DNA topoisomerase 2 gene polymorphism in dermatophytes

“…In 2017, an overview of the taxonomy of dermatophytes based on multilocus DNA sequencing has been presented by de Hoog et al 11 Their revision upgraded the taxonomical status of dermatophytes to an acceptable level of concordance among mycologists; however, their study was focused on defining the main taxonomic trends in dermatophytes and should be supplemented with more detailed investigations. Consequently, a number of recent studies have focused on the problem of species boundaries in closely related taxa, including T tonsurans and T equinum , 12 T mentagrophytes and T interdigitale 13 . Here, we present the results of partial DNA topoisomerase 2 gene ( TOP2 ) sequencing in a number of dermatophyte taxa.…”