Terbinafine-Resistant Dermatophytes Isolated in Japan

Area of Science:

• Medical Mycology
• Epidemiology
• Antimicrobial Resistance

Background:

• Terbinafine (TBF) is a widely used antifungal medication.
• Emergence of TBF-resistant dermatophytes poses a clinical challenge.
• Previous surveys in 2020 and 2022 documented TBF-resistant strains.

Purpose of the Study:

• To investigate the prevalence of TBF-resistant dermatophytes in Japan in 2023.
• To identify genetic mutations associated with TBF resistance.
• To compare current resistance rates with previous findings.

Main Methods:

• Collection of dermatophyte isolates from clinical dermatology settings in Japan.
• Antifungal susceptibility testing against TBF and other azoles.
• Sequencing of the squalene epoxidase-encoding gene in resistant isolates.

Main Results:

• 311 dermatophyte isolates were obtained, including Trichophyton interdigitale, T. indotineae, and T. rubrum.
• Ten strains (3.2%) exhibited resistance to TBF but remained susceptible to efinaconazole, itraconazole, luliconazole, and ravuconazole.
• All TBF-resistant strains harbored missense and/or deletion mutations in the squalene epoxidase gene.

Conclusions:

• The prevalence of TBF-resistant dermatophytes has increased compared to 2020 and 2022.
• Mutations in the squalene epoxidase gene are associated with TBF resistance in dermatophytes.
• Alternative antifungal agents remain effective against these resistant strains.