Disk diffusion method for fluconazole susceptibility testing of Candida albicans strains

This study evaluated the usefulness of the disk diffusion method by using different media for the susceptibility testing of fluconazole against Candida albicans strains. The susceptibility of 108 clinical isolates of C. albicans against fluconazole were determined by microdilution and disk diffusion methods by using RPMI 1640 agar and 25 microg disks. 93 of these isolates were also tested by disk diffusion technique on four different media (yeast nitrogen base agar, Sabouraud dextrose agar, Mueller Hinton agar and Mueller Hinton methylene blue agar). The results of the microdilution method were evaluated 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 optically, the best results were obtained for RPMI 1640 agar and yeast nitrogen 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 48-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 after 48 hours of incubation (89-96%). Disk diffusion method using RPMI 1640, yeast nitrogen base and Mueller Hinton methylene blue agar appears to be a useful, rapid and reliable screening technique for testing the susceptibility of C. albicans strains to fluconazole.