Abstract:

Objective To compare broth microdilution and agar dilution methods for in vitro testing of activities of fluconazole, ketoconazole and itraconazole against clinical Malassezia isolates. Methods Broth microdilution and agar dilution methods were used to determine the minimal inhibitory concentration （MIC） of fluconazole, ketoconazole and itraconazole for 27 clinical strains （5 species） of Malassezia. Results The minimal inhibitory concentration （MIC） ranges of fluconazole, ketoconazole and itraconazole were 0.25 - ≥64 mg/L, ≤0.03 - 0.5 mg/L and ≤0.03 - 0.125 mg/L respectively as shown by broth microdilution method, 2 - ≥64 mg/L, ≤0.03 - 0.5 mg/L and ≤0.03 - 0.25 mg/L respectively as revealed by agar dilution method. Both methods demonstrated that itraconazole possessed the strongest activity against Malassezia species, followed by ketoconazole and fluconazole. The agreement rate in MICs between the two methods was 78.8%, 85.2% and 88.9%, respectively for fluconazole, ketoconazole and itraconazole, with the intraclass correlation coefficients （ICCs） being 0.88, 0.80 and 0.76 respectively. Conclusions Fluconazole, ketoconazole and itraconazole are highly active against Malassezia species in vitro, and itraconazole is the most active. Broth microdilution and agar dilution method coincide well in, and are applicable for, the antifungal susceptibility testing of Malassezia species in vitro.

Key words: MIC