Antifungal Susceptibility Testing of Dermatophytes

Abstract

The 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. The microbroth dilution method was performed according to CLSI standards. In the present study, antifungal susceptibility testing was done by microdilution method of dermatophytes against five 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 0.001–0.64 μg/ml followed by ketoconazole at a MIC range 0.01–3.84 μg/ml. The itraconazole showed a MIC range 0.082–20.45 μg/ml whereas the griseofulvin and fluconazole showed a highest MIC range 0.32–5.12 μg/ml. The MIC 50 of terbinafine was low at 0.02 μg/ml followed by ketaconazole 0.24 μg/ml. The MIC 50 of itraconazole and griseofulvin was 1.28 μg/ml .The highest MIC 50 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 MIC 90 itraconazole was 2.50 μg/ml and for griseofulvin it was 2.56 μg/ml. The highest MIC 90 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.