Trends in Antifungal Susceptibility Testing Using CLSI Reference and Commercial Methods

Antifungal susceptibility testing should identify in vitro resistance among a normally susceptible population or should detect the development of resistance during therapy. The Clinical and Laboratory Standards Institute (CLSI; formerly the National Committee for Clinical Laboratory Standards [NCCLS]) has developed reproducible methods for testing the activity of antifungal agents against yeasts (the M27-A3, M27-S3, M44-A and M44-S2 documents) and filamentous fungi (molds; the M38-A2 document). The yeast documents describe both quality control (QC) and interpretative breakpoint parameters for several antifungal agents versus Candida spp. In vitro breakpoints, as well as a QC and reference strain, has been recently described for mold testing. Standard guidelines for testing echinocandins against molds, guidelines for testing dermatophytes, as well as a disk-diffusion method for molds, have been developed recently. However, standard parameters for minimum fungicidal concentration determinations and selection of QC strains and guidelines for testing Malassezia spp. are under development. Breakpoints for Cryptococcus neoformans, dermatophytes and Malassezia spp. versus any antifungal agent and for posaconazole and amphotericin B versus yeasts are not available.