Comparative evaluation of macrodilution and chromogenic agar screening for determining fluconazole susceptibility of Candida albicans

Abstract

A simple screening method for fluconazole susceptibility using CHROMagar Candida with fluconazole was compared with the National Committee for Clinical Laboratory Standards (NCCLS) macrobroth method. In this agar dilution method, susceptible Candida albicans colonies are smaller on medium with fluconazole than on fluconazole-free medium. Yeasts with decreased susceptibility have normal-sized colonies on medium containing fluconazole. On agar with 16 micrograms of fluconazole per ml, 32 of 34 strains with NCCLS MICs of > or = 16 micrograms/ml were correctly predicted, as were 66 of 68 with MICs of < 16, an agreement of 96%. On agar with 8 micrograms of fluconazole per ml, 38 of 41 isolates with MICs of > or = 8 were correctly predicted, as were 59 of 61 isolates with MICs of < 8, an agreement of 95%. This agar dilution methods appears to highly correlate with NCCLS macrobroth methods for detection of C. albicans and may be an effective screen for fluconazole susceptibility.