Disk diffusion method for fluconazole susceptibility testing of Candida albicans strains

This study evaluated the usefulness of the disk diffusion method by using d ifferent media for the susceptibility testing of fluconazole against Candid a albicans strains. The susceptibility of 108 clinical isolates of C. albic ans against fluconazole were determined by microdilution and disk diffusion methods by using RPMI 1640 agar and 25 mug disks. 93 of these isolates wer e also tested by disk diffusion technique on four different media (yeast ni trogen base agar, Sabouraud dextrose agar, Mueller Hinton agar and Mueller Hinton methylene blue agar). The results of the microdilution method were e valuated visually and optically. The disk diffusion results were determined after 24 and 48 hours of incubation. When the 24-hour zone diameters were compared to the minimal inhibitory concentrations determined visually and o ptically, the best results were obtained for RPMI 1640 agar and yeast nitro gen base agar. The correlation coefficients were r=-0.34, -0.41 and r=-0.33 , -0.32 for the first and second media, respectively. The best values (r=-0 .29, -0.39) were obtained for Mueller Hinton methylene blue agar when the 4 8-hour zone diameters were considered. Agreement between the disk diffusion and microdilution methods was best for RPMI 1640, yeast nitrogen base and Mueller Hinton methylene blue agar after 24 hours of incubation (87-89%, 88 -90%, 93-96%, respectively) and for Mueller Hinton methylene blue agar afte r 48 hours of incubation (89-96%). Disk diffusion method using RPMI 1640, y east nitrogen base and Mueller Hinton methylene blue agar appears to be a u seful, rapid and reliable screening technique for testing the susceptibilit y of C. albicans strains to fluconazole.