Drug-resistance genes and antifungal susceptibility of Trichophyton verrucosum variants isolated from bovine skin lesions and farm environments

Trichophyton verrucosum causes a highly contagious disease in bovines and is occasionally transmitted to humans. Azoles are widely used as antifungal drugs in bovines, and act by targeting the ergosterol biosynthesis pathway. However, cases of treatment failure and recurrence of dermatophyte infections have been associated with mutations at the drug target site. Currently, information on T. verrucosum variants is lacking. This study aimed to classify T. verrucosum variants isolated from animals exhibiting clinical symptoms and cattle environments in the Republic of Korea based on their antifungal susceptibility and the presence or absence of ergosterol biosynthesis (ERG) and subtilisin genes. Of 139 clinical and 39 environmental samples, 86 and 21 were found to be infected, respectively. The positivity rate of calves aged 1–6 months was 73.1%, which was significantly higher than that of calves aged >6 months (55.2%). Twenty-seven T. verrucosum strains were identified as T. album (n = 9), T. ochraceum (n = 6), and T. discoides (n = 12). Antifungal susceptibility testing showed that enilconazole had the lowest geometric mean antifungal activity of 1.08, 1, and 0.94 µg/ml against T. album, T. ochraceum, and T. discoides, respectively. The detection ratios of ERG3 and ERG6 differed significantly among the three variants. In conclusion, our study suggests conducting sample cultures and antifungal susceptibility tests on isolates before administering antifungal drugs. Moreover, the expression profile of ERG appears to have a potential link to drug susceptibility. This information may contribute to the prevention and management of dermatophytosis in cattle.