BACKGROUND: The Trichophyton mentagrophytes complex encompasses common dermatophytes causing superficial mycoses in humans and animals. The taxonomy of the complex is unstable, with conflicting views on the species status of some taxa, particularly T. indotineae and T. interdigitale. Due to the presence of intermediate genotypes, neither MALDI-TOF MS nor ITS rDNA sequencing can accurately distinguish all taxa in the complex, potentially contributing to clinical misdiagnoses. OBJECTIVES: This research resolves phylogenetic relationships within the T. mentagrophytes complex. Based on these data, the taxonomical recommendations are suggested. METHODS: In order to resolve the phylogenetic relationship of the T. mentagrophytes complex, we employed Restriction Site-Associated DNA Sequencing (RADseq) to produce a high-resolution single nucleotide polymorphism (SNP) dataset from 95 isolates. The SNP-based analyses indicated the presence of two major genetic clusters corresponding to T. mentagrophytes (including T. indotineae) and T. interdigitale. RESULTS: Our results challenge the species status of T. indotineae because of insufficient genetic divergence from T. mentagrophytes. Therefore, we propose designating T. indotineae as T. mentagrophytes var. indotineae (or T. mentagrophytes ITS genotype VIII) to avoid further splitting of the complex and taxonomic inflation. Although T. interdigitale shows clearer genetic differentiation, its separation is incomplete and identification of some isolates is ambiguous when using routine methods, leading us to consider it a variety as well: T. mentagrophytes var. interdigitale. CONCLUSIONS: We recommend using T. mentagrophytes as the overarching species name for all complex isolates. Where precise molecular identification is possible, the use of variety ranks is encouraged. Since identical resistance mechanisms are not specific to any genotype or dermatophyte species, identifying antifungal resistance is more important than differentiating closely related genotypes or populations.

• Keywords
• Trichophyton interdigitale, Trichophyton mentagrophytes, anthropophilic dermatophytes, antifungal resistance, dermatophytosis, population structure, taxonomy, zoophilic dermatophytes,
• MeSH
• Antifungal Agents * pharmacology   MeSH
• Arthrodermataceae * genetics   classification   drug effects   MeSH
• DNA, Fungal genetics   MeSH
• Phylogeny * MeSH
• Genomics methods   MeSH
• Genotype MeSH
• Polymorphism, Single Nucleotide MeSH
• Humans MeSH
• Sequence Analysis, DNA MeSH
• Tinea microbiology   MeSH
• Trichophyton * genetics   classification   drug effects   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Antifungal Agents * MeSH
• DNA, Fungal MeSH

The clinical diagnosis of dermatophytosis and identification of dermatophytes face challenges due to reliance on culture-based methods. Rapid, cost-effective detection techniques for volatile organic compounds (VOCs) have been developed for other microorganisms, but their application to dermatophytes is limited. This study explores using VOCs as diagnostic markers for dermatophytes. We compared VOC profiles across different dermatophyte taxa using solid-phase microextraction (SPME) and advanced analytical methods: gas chromatography-mass spectrometry (GC-MS) and comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS). We analyzed 47 dermatophyte strains from 15 taxa grown on sheep wool, including clinically significant species. Additionally, we examined phylogenetic relationships among the strains to correlate genetic relatedness with metabolite production. Our results showed that GC×GC-TOFMS offered superior resolution but similar differentiation of VOC profiles compared to GC-MS. VOC spectra allowed reliable distinction of taxonomic units at the species level and below, however, these distinctions showed only a slight correlation with phylogenetic data. We identified pan-dermatophyte and species- or strain-specific VOC profiles, indicating their potential for rapid, non-invasive detection of dermatophyte infections, including epidemic strains. These patterns could enable future taxa-specific identification. Our study highlights the potential of VOCs as tools for dermatophyte taxonomy and diagnosis.

• Keywords
• Dermatophytes, Gas chromatography-mass spectrometry, Metabolite profiles, Volatile organic compounds,
• MeSH
• Arthrodermataceae * classification   isolation & purification   genetics   MeSH
• Phylogeny * MeSH
• Humans MeSH
• Solid Phase Microextraction MeSH
• Odorants analysis   MeSH
• Sheep MeSH
• Gas Chromatography-Mass Spectrometry * MeSH
• Volatile Organic Compounds * analysis   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Volatile Organic Compounds * MeSH

This study looked for correlations between molecular identification, clinical manifestation, and morphology for Trichophyton interdigitale and Trichophyton mentagrophytes. For this purpose, a total of 110 isolates were obtained from Czech patients with various clinical manifestations of dermatophytosis. Phenotypic characters were analyzed, and the strains were characterized using multilocus sequence typing. Among the 12 measured/scored phenotypic features, statistically significant differences were found only in growth rates at 37 °C and in the production of spiral hyphae, but none of these features is diagnostic. Correlations were found between T. interdigitale and higher age of patients and between clinical manifestations such as tinea pedis or onychomychosis. The MLST approach showed that internal transcribed spacer (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 matrix-assisted laser desorption/ionization time-of-flight mass spectrometry fail to distinguish these species. To avoid further confusion and to 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 Trichophyton indotineae is possible based on molecular data, we recommend optionally using a variety rank: T. mentagrophytes var. interdigitale and T. mentagrophytes var. indotineae.

Species in the T. mentagrophytes complex lack support from usual taxonomic methods and simple identification tools are missing or inaccurate. To avoid recurring confusions, we propose naming the entire complex as T. mentagrophytes and optionally use rank variety to classify the observed variability.

• Keywords
• anthropophilic dermatophytes, dermatophytosis, multigene phylogeny, skin infections, zoophilic dermatophytes,
• MeSH
• Arthrodermataceae MeSH
• DNA, Fungal genetics   chemistry   MeSH
• Phenotype MeSH
• Phylogeny MeSH
• DNA, Ribosomal Spacer genetics   chemistry   MeSH
• Multilocus Sequence Typing veterinary   MeSH
• Sequence Analysis, DNA veterinary   MeSH
• Tinea * diagnosis   veterinary   MeSH
• Trichophyton MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• DNA, Fungal MeSH
• DNA, Ribosomal Spacer MeSH