Clinical utility of in vitro antifungal susceptibility testing

The incidence of fungal and yeast infections, especially Candida and Aspergillus, as well as other newer fungal infections has increased considerably in recent years. Treatment failures are due to microbiological or clinical resistance, the latter being related to the drug, host factors, the fungus and the therapeutic procedures. An overview of efforts to find correlations between microbiological and clinical resistance is presented. The NCCLS M27-A consensus document for in vitro susceptibility testing of Candida and Cryptococcus is a good attempt at this, as is the M38-P for some filamentous fungi. The data available thus far indicate that there is a relationship between in vitro resistance and clinical failure, but not between in vitro susceptibility and therapeutic success. Furthermore, the breakpoints (MIC) that can be applied to the susceptibility tests are established based more on the resistance limits than on susceptibility. MIC data are also essential to obtain distribution profiles of MIC values for fungal populations and for future correlations of MICs with clinical response.