EUCAST Definitive Document EDef 7.1: method for the determination of broth dilution MICs of antifungal agents for fermentative yeasts: Subcommittee on Antifungal Susceptibility Testing (AFST) of the ESCMID European Committee for Antimicrobial Susceptibility Testing (EUCAST)∗

Abstract

INTRODUCTIONAntifungal susceptibility tests are performed onfungi that cause disease, especially if they belongto a species exhibiting resistance to commonlyused antifungal agents. Antifungal susceptibilitytesting is also important for resistance surveil-lance, for epidemiological studies and forcomparing the in-vitro activity of new and exist-ing agents.Dilution methods are used to establish theMICs of antimicrobial agents. These are thereference methods for antimicrobial susceptibilitytesting, and are used mainly to establish theactivity of a new antifungal agent, to confirm thesusceptibility of organisms that give equivocalresults in routine tests, and to determine thesusceptibility of fungi where routine dilution testsmay be unreliable. Fungi are tested for theirability to produce visible growth in microdilutionplate wells containing broth culture media andserial dilutions of the antifungal agents (brothmicrodilution). The MIC is defined as the lowestconcentration (in mg⁄L) of an antifungal agentthat inhibits the growth of a fungus. The MICprovides information concerning the susceptibil-ity or resistance of an organism to the antifungalagent and can help in making correct treatmentdecisions.The method described in this document isintended for testing the susceptibility ofyeasts that cause clinically significant infections(primarily Candida spp.). The method encom-passes only those yeasts that are able to fermentglucose. Thus, the susceptibility of non-fermenta-tive yeasts, e.g., Cryptococcus neoformans, cannotbe determined by the current procedure, and themethod is not suitable for testing the yeast formsof dimorphic fungi.SCOPEThe standard method described in this documentprovides a valid method for testing the suscepti-bility of glucose-fermenting yeasts to antifungalagents by determination of the MIC. MICs indi-cate the activity of a given antifungal drug underthe described test conditions, and can be used inmaking decisions concerning patient manage-ment after taking into account other factors, e.g.,pharmacokinetics, pharmacodynamics and resis-tance mechanisms. The MIC also allows fungi tobe categorised as ‘susceptible’ (S), ‘intermediate’(I) or ‘resistant’ (R) to a drug. In addition, MICdistributions can be used to define wild-type ornon-wild-type fungal populations.This method is intended primarily to facilitatean acceptable degree of conformity, i.e., agree-ment within specified ranges among laboratories,in measuring the susceptibility of yeasts to anti-fungal agents. The method is designed to be easyto perform, rapid, economical, and suitable forreading by microdilution plate readers in order toallow direct transfer, storage and manipulation ofthe data by computer. The method is alsointended to yield results that are concordantwith those obtained using the procedure