A patient with extensive tinea corporis (involving >30% BSA) has failed two courses of topical antifungals and one course of griseofulvin. KOH examination consistently shows arthroconidia-forming hyphae. Which change in the pathogen's susceptibility profile most commonly accounts for treatment failure in India currently?

• A Overexpression of efflux pumps conferring azole resistance
• B Biofilm formation by Trichophyton tonsurans
• C Mutation in the squalene epoxidase gene (ERG1) conferring terbinafine resistance ✓
• D Selection of a non-dermatophyte mould replacing T. rubrum

Explanation

India is experiencing a pandemic of difficult-to-treat tinea, predominantly due to T. indotineae (formerly hypervirulent T. mentagrophytes genotype VIII), which harbours mutations in the ERG1 gene (encoding squalene epoxidase — the target of terbinafine). These mutations cause high MIC to terbinafine (minimum inhibitory concentration >0.5 µg/mL), making standard terbinafine therapy ineffective. These strains remain susceptible to itraconazole. Azole efflux pump overexpression is more relevant in Candida species. Correct identification by ITS sequencing and antifungal susceptibility testing is essential.

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.