Susceptibility Testing of Fluconazole by the NCCLS Broth Macrodilution Method, E-Test, and Disk Diffusion for Application in the Routine Laboratory

Antifungal susceptibility testing may be an important aid in the treatment of patients with life-threatening yeast infections. In order to establish the suitability of different susceptibility test methods for fluconazole with yeasts, the Rosco tablet and the E-test were compared with the gold standard NCCLS broth macrodilution method for 106 yeast strains. These included 102 clinical isolates of Candida spp., including Candida glabrata (n = 30), Candida albicans (n = 20), Candida tropicalis (n = 13), Candida parapsilosis (n = 10), Candida krusei (n = 8), plus Cryptococcus neoformans (n = 3), Saccharomyces cerevisiae (n = 2), and 16 strains belonging to other Candida spp. Four American Type Culture Collection strains of Candida were included as quality controls. The NCCLS method was found to be too complex and labor-intensive for routine testing. The E-test is an accurate alternative, but experience in determining MICs and careful attention to procedural details are critically important. The Rosco tablet showed the best agreement with the NCCLS reference method, especially when newly established breakpoints of R ≤ 10 mm and S ≥ 21 mm were used.