Resolving the taxonomy of emerging zoonotic pathogens in the Trichophyton benhamiae complex

Abstract

Species of the Trichophyton benhamiae complex are predominantly zoophilic pathogens with a worldwide distribution. These pathogens have recently become important due to their epidemic spread in pets and pet owners. Considerable genetic and phenotypic variability has been revealed in these emerging pathogens, but the species limits and host spectra have not been clearly elucidated. In this study, we used an approach combining phylogenetic analysis based on four loci, population-genetic data, phenotypic and physiological analysis, mating type gene characterization and ecological data to resolve the taxonomy of these pathogens. This approach supported the inclusion of nine taxa in the complex, including three new species and one new variety. Trichophyton benhamiae var. luteum var. nov. (“yellow phenotype” strains) is currently a major cause of zoonotic tinea corporis and capitis in Europe (mostly transmitted from guinea pigs). The isolates of the “white phenotype” do not form a monophyletic group and are segregated into three taxa, T. benhamiae var. benhamiae (mostly North America; dogs), T. europaeum sp. nov. (mostly Europe; guinea pigs), and T. japonicum sp. nov. (predominant in East Asia but also found in Europe; rabbits and guinea pigs). The new species T. africanum sp. nov. is proposed for the “African” race of T. benhamiae. The introduction to new geographic areas and host jump followed by extinction of one mating type gene have played important roles in the evolution of these pathogens. Due to considerable phenotypic similarity of many dermatophytes and phenomena such as incomplete lineage sorting or occasional hybridization and introgression, we demonstrate the need to follow polyphasic approach in species delimitation. Neutrally evolving and noncoding DNA regions showed significantly higher discriminatory power compared to conventional protein-coding loci. Diagnostic options for species identification in practice based on molecular markers, phenotype and MALDI-TOF spectra are presented. A microsatellite typing scheme developed in this study is a powerful tool for the epidemiological surveillance of these emerging pathogens.