Dermatophyte susceptibilities to antifungal azole agents tested in vitro by broth macro and microdilution methods

Abstract

The in vitro susceptibility of dermatophytes to the azole antifungals itraconazole, fluconazole and ketoconazole was evaluated by broth macro and microdilution methods, according to recommendations of the CLSI, with some adaptations. Twenty nail and skin clinical isolates, four of Trichophyton mentagrophytes and 16 of T. rubrum were selected for the tests. Itraconazole minimal inhibitory concentrations (MIC) varied from < 0.03 to 0.25 μg/mL in the macrodilution and from < 0.03 to 0.5 μg/mL in the microdilution methods; for fluconazole, MICs were in the ranges of 0.5 to 64 μg/mL and 0.125 to 16 μg/mL by the macro and microdilution methods, respectively, and from < 0.03 to 0.5 μg/mL by both methods for ketoconazole. Levels of agreement between the two methods (± one dilution) were 70% for itraconazole, 45% for fluconazole and 85% for ketoconazole. It is concluded that the strains selected were inhibited by relatively low concentrations of the antifungals tested and that the two methodologies are in good agreement especially for itraconazole and ketoconazole.