Standardized disk diffusion method for yeasts

Worldwide, the most commonly used technique for antibacterial susceptibility testing is the disk diffusion test. However, disk diffusion testing of antifungal agents has been slow to develop despite the fact that early studies with fluconazole disks showed promise for testing Candida spp. To make antifungal susceptibility testing more readily available to clinical microbiology laboratories, the Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS) has proposed a standardized disk diffusion method for susceptibility testing of Candida spp. Although the Subcommittee has established quality control disk parameters for fluconazole, voriconazole, and posaconazole, zone interpretive criteria (breakpoints) are only available for fluconazole and voriconazole. Therefore, the clinical relevance for any other (than fluconazole and voriconazole) drug-organism combinations is uncertain. The design of the disk diffusion method for Candida spp. is similar to that for bacteria using the same medium (Mueller-Hinton agar), but supplemented with glucose and methylene blue dye. Other specific testing guidelines are summarized below. A commercial method, similar to the CLSI M44-A method, that uses a 9-mm tablet instead of the 6-mm disk is also available in Europe.