Epidemiology and Molecular Identification of Dermatophytes: Focus on the Detection of the Emerging Species Trichophyton indotineae in Northern Italy

Background: Trichophyton indotineae, a new emerging pathogen according to the WHO, is known to cause severe forms of tinea. Given that traditional identification methods rely on morphological characteristics, and the morphological distinctions among T. indotineae, T. mentagrophytes, and T. interdigitale are minimal, the adoption of alternative diagnostic techniques, such as RT-PCR or gene sequencing, has become critically important to prevent misidentification. The purpose of this study was firstly to analyze the local epidemiology of dermatophytes isolated and secondly to investigate the presence of T. indotineae among the isolated strains. Methods: Between January 2021 and June 2024, 1096 samples of skin adnexa were analysed. The isolated strains belonging to the genus Trichophyton were submitted to molecular identification by ITS sequencing, and T. indotineae strains were subjected to squalene epoxidase (SQLE) sequencing analysis. Results: Trichophyton rubrum and Trichophyton interdigitale appear to be the most prevalent pathogenic species. Molecular identification reveals four T. indotineae strains (4/87; 4.61%) from Asian patients, which were also characterized by gene mutations associated with terbinafine resistance. Conclusions: This study has made it clear that there is a need to implement basic mycological diagnostics with molecular methods to avoid misidentifications, ensure the correct identification, and evaluate the presence of mutations associated with antifungal drug resistance.