In Vitro Antifungal Susceptibility Testing of 5 Antifungal Agents against Dermatophytic Species by CLSI (M38-A) Micro Dilution Method

Cases of dermatophytoses have increased over the past few decades. In the last few years, a number of newer less toxic antifungal drugs have become available for clinical use. The increased use of antifungal, often for prolonged periods, has led to the recognition of the phenomenon of acquired antifungal resistance among previously susceptible strains or species and to the increased incidence of infections with less common species. Our study mainly focused on the in vitro susceptibility of clinical isolates of dermatophytes against frequently used 5 antifungal agents. The microbroth dilution method was performed according to CLSI standards. In the present study antifungal susceptibility testing was done by micro dilution method of dermatophytes against 5 antifungal agents namely, ketoconazole (imidazoles) fluconazole, itraconazole (triazoles), griseofulvin and terbinafine and their activity against significant number of strains, representing a wide spectrum of dermatophyte species is assessed.

Dermatophytic strains: A total of 119 strains of dermatophytes belonging to 10 species were tested. They were T. rubrum (n=40), T. mentagrophytes (n=19), T. violaceum (n=15), M. gypseum (n=12), E. flocossum (n=9), M. audouinii (n=8), T. schoenleinii (n=5), M. canis (n=5), T. tonsurans (n=4) and T. verrucosum (n=2). The MIC ranges of all the 119 isolates of dermatophytes tested for antifungal susceptibility showed that terbinafine had the lowest MIC range of 0.001 to 0.64 μg/ml followed by ketoconazole at a MIC range of 0.01-3.84 μg/ml. The itraconazole showed a MIC range of 0.082-20.45 μg/ml whereas the griseofulvin and fluconazole showed a highest MIC range of 0.32-5.12 μg/ml. The MIC50 of Terbinafine was low at 0.02 μg/ml followed by Ketaconazole 0.24 μg/ml. The MIC50 of itraconazole and griseofulvin was1.28 μg/ml .The highest MIC50 with 2.56 μg/ml was recorded for Fluconazole. The MIC90 of terbinafine was low at 0.32 μg/ml followed by Ketaconazole with 1.92 μg/ml. The MIC90 Itraconazole was 2.50 μg/ml and for griseofulvin it was 2.56 μg/ml. The highest MIC90 of flucanozole was high at 10.24 μg/ml. In our study, we observed that terbinafine had the lowest MIC values compared to ketoconazole, itraconazole, griseofulvin and fluconazole. Hence the efficacy of terbinafine is higher followed by ketoconazole when compared with other drugs. This study helps in choosing a right antifungal drug for treating tinea infections.