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Antifungal Susceptibility Testing of Dermatophytes

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Antifungal Susceptibility Testing of Dermatophytes
Mahmoud Ghannoum, PhD
Dermatology Online Journal 7(1): 23C

Center For Medical Mycology, University Hospitals of Cleveland and Case western Reserve University, Cleveland, Ohio

A standardized reference method for dermatophyte in vitro susceptibility testing is lacking. To establish such a method we initiated a research program where the optimal medium and other growth variables were selected. To select which agar medium best supported conidial growth, representative isolates of dermatophytes were grown on different agars. Preliminary experiments showed only oatmeal cereal agar supported the production of conidia by Trichophyton rubrum. We tested the ability of 251 T. rubrum isolates to form conidia using three different cereal agars and potato dextrose agar. Overall, oatmeal cereal agar and rice media were comparable in their abilities to support conidial growth of T. rubrum. Next, we used the oatmeal cereal agar for conidial formation along with the optimal conditions for dermatophyte susceptibility testing identified earlier and determined the antifungal susceptibility of 217 dermatophytes against fluconazole, griseofulvin, itraconazole and terbinafine. Relative to other agents tested terbinafine possessed the highest antifungal activity against all of the dermatophytes. The mean MIC± SEM (µg/ml) values for fluconazole, itraconazole, terbinafine and griseofulvin were: 2.07± 0.29, 0.13 ± 0.01, 0.002 ± 0.0003, 0.71 ± 0.05, respectively. This study is the first step in the identification of optimal conditions that could be used in the standardization of the antifungal susceptibility testing method for dermatophytes. Inter and intralaboratory agreement as well as clinical correlations need to be established.

© 2001 Dermatology Online Journal