Terbinafine-resistant Trichophyton indotineae and SQLE mutations in human and animal dermatophytosis: a One Health perspective
Abstract
BackgroundDermatophytosis is an increasing public health and veterinary concern amid the emergence of terbinafine-resistant dermatophytes and recurrent treatment failures. This study characterized dermatophyte isolates from human and animal cases, assessed their antifungal susceptibility, and investigated terbinafine resistance-associated mutations in the squalene epoxidase (SQLE) gene.MethodsTwenty-two Trichophyton mentagrophytes complex isolates were recovered from skin scrapings of patients with recurrent tinea corporis and tinea cruris, and 39 isolates were obtained from animals with clinical signs of ringworm. Isolates were identified by sequencing the internal transcribed spacer (ITS) region, and antifungal susceptibility was determined by broth microdilution method. The SQLE gene was sequenced to detect resistance-associated substitutions.ResultsAll human isolates were identified as Trichophyton indotineae; animal isolates comprised T. mentagrophytes, T. verrucosum, Microsporum canis, and one feline-derived T. rubrum isolate. Fluconazole resistance occurred among both human and animal isolates, but terbinafine resistance was largely confined to human-derived T. indotineae, while most animal isolates, particularly T. verrucosum and M. canis, remained susceptible. SQLE sequencing identified several resistance-associated substitutions: Phe397Leu, the most frequent mutation in T. indotineae, was consistently linked to elevated terbinafine MICs (0.5–16 μg/mL), and Gln408Leu was associated with an MIC of 8 μg/mL and pronounced growth on terbinafine-containing medium. Resistance-associated substitutions were also detected in animal isolates, including Leu393Ser (T. rubrum) and Ile415Ser (T. mentagrophytes), both recovered from cats. Three isolates carried two concurrent substitutions, Phe397Leu and Ala448Thr. ITS-based phylogenetic analysis demonstrated that the studied human clinical isolates clustered with genetically related isolates from multiple countries, with no evident geographic segregation, suggesting widespread dissemination of closely related T. indotineae genotypes.ConclusionTerbinafine-resistant T. indotineae predominates among human dermatophyte isolates, driven largely by SQLE mutations, especially Phe397Leu. The presence of resistance-associated SQLE mutations in animal-derived dermatophytes indicates spillover of human-adapted resistant lineages into companion animals, underscoring the need for integrated antifungal susceptibility testing and One Health-based surveillance.
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BibTeX
@article{taha2026terbinafineresistant,
title = {{Terbinafine-resistant Trichophyton indotineae and SQLE mutations in human and animal dermatophytosis: a One Health perspective}},
author = {Mohamed Taha and Safaa A. Abdallah and Mohamed S. A. Zaki and Abdulah J. Alqahtani and Asmaa Shaker and Yasmine H. Tartor},
journal = {Frontiers in Microbiology},
year = {2026},
month = nov,
doi = {10.3389/fmicb.2026.1974916},
url = {https://www.frontiersin.org/articles/10.3389/fmicb.2026.1974916},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Terbinafine-resistant Trichophyton indotineae and SQLE mutations in human and animal dermatophytosis: a One Health perspective
AU - Mohamed Taha
AU - Safaa A. Abdallah
AU - Mohamed S. A. Zaki
AU - Abdulah J. Alqahtani
AU - Asmaa Shaker
AU - Yasmine H. Tartor
PY - 2026
DA - 2026/11/05
JO - Frontiers in Microbiology
DO - 10.3389/fmicb.2026.1974916
UR - https://www.frontiersin.org/articles/10.3389/fmicb.2026.1974916
AB - BackgroundDermatophytosis is an increasing public health and veterinary concern amid the emergence of terbinafine-resistant dermatophytes and recurrent treatment failures. This study characterized dermatophyte isolates from human and animal cases, assessed their antifungal susceptibility, and investigated terbinafine resistance-associated mutations in the squalene epoxidase (SQLE) gene.MethodsTwenty-two Trichophyton mentagrophytes complex isolates were recovered from skin scrapings of patients with recurrent tinea corporis and tinea cruris, and 39 isolates were obtained from animals with clinical signs of ringworm. Isolates were identified by sequencing the internal transcribed spacer (ITS) region, and antifungal susceptibility was determined by broth microdilution method. The SQLE gene was sequenced to detect resistance-associated substitutions.ResultsAll human isolates were identified as Trichophyton indotineae; animal isolates comprised T. mentagrophytes, T. verrucosum, Microsporum canis, and one feline-derived T. rubrum isolate. Fluconazole resistance occurred among both human and animal isolates, but terbinafine resistance was largely confined to human-derived T. indotineae, while most animal isolates, particularly T. verrucosum and M. canis, remained susceptible. SQLE sequencing identified several resistance-associated substitutions: Phe397Leu, the most frequent mutation in T. indotineae, was consistently linked to elevated terbinafine MICs (0.5–16 μg/mL), and Gln408Leu was associated with an MIC of 8 μg/mL and pronounced growth on terbinafine-containing medium. Resistance-associated substitutions were also detected in animal isolates, including Leu393Ser (T. rubrum) and Ile415Ser (T. mentagrophytes), both recovered from cats. Three isolates carried two concurrent substitutions, Phe397Leu and Ala448Thr. ITS-based phylogenetic analysis demonstrated that the studied human clinical isolates clustered with genetically related isolates from multiple countries, with no evident geographic segregation, suggesting widespread dissemination of closely related T. indotineae genotypes.ConclusionTerbinafine-resistant T. indotineae predominates among human dermatophyte isolates, driven largely by SQLE mutations, especially Phe397Leu. The presence of resistance-associated SQLE mutations in animal-derived dermatophytes indicates spillover of human-adapted resistant lineages into companion animals, underscoring the need for integrated antifungal susceptibility testing and One Health-based surveillance.
SN - 1664-302X
ER -