Fluconazole disk diffusion susceptibility testing of Candida species

We describe a simple procedure for detecting fluconazole-resistant yeasts by a disk diffusion method. Forty clinical Candida sp. isolates were tested on RPMI-glucose agar with either 25- or 50-mu g fluconazole disks. With 25-mu g disks, zones of inhibition of greater than or equal to 20 mm at 24 h accurately identified 29 of 29 isolates for which MICs were 18 mu g/ml, and with 50-mu g disks, zones of greater than or equal to 27 mm identified 28 of 29 such isolates. All 11 isolates for which MICs were >8 mu g/ml were identified by using either disk. Disk diffusion may be a useful screening method for clinical microbiology laboratories.