Antifungal susceptibility testing and clinical efficacy observation of methylene blue photodynamic therapy in treating trichophyton indotineae infections

Superficial fungal infections caused by Trichophyton indotineae are spreading globally, with mutations in its SQLE gene (F397L/L393S) increasing resistance to traditional antifungals like terbinafine, creating an urgent need for new therapies. This study evaluated the clinical efficacy of methylene blue-mediated photodynamic therapy (MB-PDT). In vitro susceptibility testing was performed on a multidrug-resistant T. indotineae strain isolated from a 25-year-old Indian male with extensive skin lesions (confirmed by ITS sequencing). A randomized controlled trial was conducted: the experimental group (forearm lesions) received topical 1 % methylene blue plus 630 ± 5 nm red light irradiation (100 J/cm², once weekly for 4 weeks), while the control group (other lesions) were treated with topical 1 % terbinafine cream twice daily. Results showed the strain was highly sensitive to methylene blue (MIC = 1.0 μg/mL) but resistant to terbinafine (MIC = 8.0 μg/mL). After 2 weeks, the experimental group achieved scaling resolution and negative fungal microscopy, with sustained efficacy at 4 weeks; the control group retained residual hyphae. Conclusion: MB-PDT rapidly eradicates drug-resistant T. indotineae infections, outperforming traditional topical agents and providing a safe, effective alternative for drug-resistant dermatophytosis.