Molecular characterization of Trichophyton indotineae causing dermatophytosis in South India: a case series

Abstract

Background. Dermatophytes are commonly encountered causes of superficial fungal infections of the skin, nails, and hair. Dermatophyte fungi are keratinophilic fungi, which include Trichophyton, Epidermophyton, and Microsporum. These fungal pathogens can be transmitted from animals (livestock and pets) to humans. In recent years, there has been a significant epidemiological shift toward infections caused by Trichophyton indotineae, an emerging dermatophyte species frequently associated with persistent infections and reduced susceptibility to terbinafine. Accurate species identification using molecular methods is essential because conventional phenotypic techniques cannot reliably distinguish members of the Trichophyton mentagrophytes–T. interdigitale species complex. Case presentation. We report five culture-confirmed cases of dermatophytosis in adults presenting with tinea corporis, tinea cruris, and tinea faciei. Diagnosis was established by direct microscopy using 10% potassium hydroxide (KOH), fungal culture on Sabouraud dextrose agar and Dermatophyte Test Medium, lactophenol cotton blue microscopy, urease testing, and potato dextrose agar slide culture. Molecular identification was performed by ITS sequencing followed by BLAST analysis, and all five isolates were identified as Trichophyton indotineae. The nucleotide sequences were deposited in GenBank under accession numbers PX457641–PX457645. Conclusion. This case series highlights the emerging clinical importance of molecularly confirmed Trichophyton indotineae as a cause of dermatophytosis in South India. The integration of conventional mycology and molecular identification improves diagnostic accuracy and contributes valuable epidemiological information regarding this emerging dermatophyte.