Clinical and Laboratory Standards Institute guideline M44—Method for Antifungal Disk Diffusion Susceptibility Testing of Yeasts provides an approved method for determining zone diameter breakpoints for select Candida spp. with antifungal agents after 24 hours incubation, as well as quality control parameters for the same agents. This guideline fulfills the need for an alternative to the broth microdilution testing procedure (see CLSI document M27) and describes a simple, rapid, and cost-effective approach for determining fungal organisms’ susceptibility to various classes of antifungal agents. It also makes antifungal susceptibility testing more readily available to the medical microbiology laboratory and encourages the development of disk diffusion testing for newly discovered antifungal agents.

This guideline replaces the previous edition of the approved guideline, M44-A2, published in 2009. Several changes were made in this edition, including:

• Reorganized to fit the CLSI quality management system and path of workflow format

• Revised definitions for interpretive categories to align with other CLSI susceptibility testing documents

• Added disk diffusion standards for micafungin

• Described the specific Candida spp. for which there are zone diameter breakpoints and interpretive categories

• Updated yeast nomenclature 

• Updated references to the previous informational supplement (M44-S3) to reflect CLSI document M60,4 the new supplement for broth dilution and disk diffusion yeast susceptibility testing

This guideline provides an established methodology for disk diffusion testing of select Candida spp. For zone diameter breakpoints, interpretive categories, and recommended QC ranges for caspofungin, micafungin, fluconazole, and voriconazole, refer to CLSI document M60.4 The method described is intended for testing select Candida spp. This method is not currently applicable to any other genera and has not been used in studies of the yeast form of dimorphic fungi (eg, Blastomyces dermatitidis or Histoplasma capsulatum). Moreover, testing of filamentous fungi (ie, moulds) is not covered in the current procedure.

The method described in this guideline must be followed exactly to obtain reproducible results. When new problems are recognized or improvements in these criteria are developed, changes will be incorporated into future editions of M44 and new breakpoint information will be distributed in periodic informational supplements (see CLSI document M604). This guideline is intended for use by, among others, health care, academic, government, industry, or independent research organizations that perform antifungal susceptibility testing of yeasts.