Abstract

Various susceptibility tests have been used to determine minimal inhibition concentration (MIC) of dermatophytes. They have limitations to apply practically because they need long time to determine MiC. Authors examined MIC of T. rubrum to ketoconazole and itraconazole using 96- well microplate and 24-well macroplate by method of Granade and Artis and tried to check the possibility of this method on clinical application. Nine strains of T. rubrum from patients with dermatophytosis were used. Evaluations of the factors affecting MIC were also tried. The results as follows. 1. Effect of inoculation density on determination time and MIC: Determination of MIC were possible in 4th days after inoculation at higher inoculation density (aborbance 2.0, 1.0) compared to 6th days at lower inoculation density (absorbance 0.5, 0.25). 2. Effect of incubation temperature on MIC: When incubating at 37℃, MIC were below 0.006-0.04µg/ml to ketoconazole and below 0.006-0.04µg/ml to itraconazole while at 25℃ 0.08-5.68µ8/ml to ketoconazole and 0.006-0.71µg/ml to itraconazole. Significant reduction of MIC was observed at 37℃ compared to 25℃. 3. Effect of container size on determination time and MIC: When incubating in 96–well microplate and 24-well macroplate, determination of MIC was possible in 4th to 6th days after inoculation in broth-containig 96-well microplate compared to 8th to 12th days in broth-containing 24-well macroplate. But no difference in MIC was observed between different container size. 4. Effect of media on MIC: When using broth as media, MIC were below 0.006-5.68µg/ml to ketoconazole, below 0.006-0.36µg/ml to itraconazole in broth-containg 24-well macroplate. When using agar as media, MIC were below 0.006-5.68 µg/ml to ketoconazole, below 0.006-5.68 µg/ ml to itraconazole in agar-containing 24-well macroplate. 5. These findings confirm that determination of MIC of dermatophtes by method of Granade and Artis is fast and simple technique for antifungal susceptibility test.

• Keywords: MIC (minimal inhibition concentration);Microculture;Trichophyton rubrum;Ketoconazole;Itraconazole;