In vitro antifungal susceptibility methods and clinical implications of antifungal resistance

As new antifungal agents are introduced for the treatment of infections cau sed by yeasts and filamentous fungi (moulds), it is important that reliable methods are available for the in vitro testing of both new and established agents. The ultimate goal of in vitro testing is the prediction of the cli nical outcome of therapy. The use of the M27-A procedures that were develop ed by the US National Committee for Clinical Laboratory Standards (NCCLS) h as led to increased interlaboratory agreement of minimum inhibitory concent rations (MICs) for yeasts and has facilitated the establishment of interpre tive breakpoints for fluconazole and itraconazole. The clinical relevance a nd limitations of these breakpoints are discussed elsewhere. The focus of t his paper is to review the advantages and disadvantages of the available me thods for antifungal susceptibility testing of yeasts and moulds as well as the clinical implications of in vitro antifungal resistance.