Comparative study of disc diffusion and microdilution methods in susceptibility testing of micafungin against Candida species

Objectives: To compare the Clinical Laboratory Standards Institute CLSI M44-A disc diffusion (DD) and M27-A2 broth microdilution (MD) methods for determining the susceptibility of Candida spp. to micafungin (FK463). Patients and methods: A total of 355 clinical yeast isolates including 270 Candida albicans, 45 Candida glabrata, 24 Candida krusei, 11 Candida tropicalis and 5 Candida parapsilosis were studied. The MIC of micafungin was determined by following the CLSI M27-A2 guidelines (MD). Endpoints were defined as the lowest concentration of micafungin resulting in partial inhibition (IC50) of visual growth after 24/48 h of incubation at 35 degrees C. Final concentrations were 0.008-4 mg/L of micafungin. DD testing was performed using a CLSI M44-A document with 2.5 mu g micafungin discs. Zone diameter endpoints were read after 24/48 h of incubation at 35 degrees C. Arbitrary breakpoints were 4 mg/L for MD and 15 mm for DD. Results: The best correlation was observed when we read MD 48 h/DD 24 and 48 h (97%). When the reading was MD 24 h/DD 24 and 48 h the percentage of correlation was 95.2%. Conclusions: The DD method performs well for testing the susceptibility of Candida spp. to micafungin. More studies involving more Candida strains with elevated MIC values are needed.