Intra- and Interlaboratory Agreement in Assessing the In Vitro Activity of Micafungin against Common and Rare Candida Species with the EUCAST, CLSI, and Etest Methods

The emergence of resistant strains among common and rareCandida species necessitates continuous monitoring of thein vitro susceptibilities of those isolates. We therefore assessed thein vitro activities of micafungin against 1,099 molecularly identified isolates belonging to 5 common and 20 rareCandida species by the EUCAST, CLSI, and Etest methods, assessing both the intralaboratory agreement and the interlaboratory agreement for two centers. The median micafungin EUCAST MICs were as follows, from the lowest to the highest: forCandida albicans , 0.004 mg/liter; forC. glabrata , 0.016 mg/liter; forC. tropicalis , 0.031 mg/liter; forC. krusei , 0.125 mg/liter; forC. parapsilosis , 2 mg/liter. Among rareCandida species, high MICs were found forC. guilliermondii ,C. lipolytica ,C. orthopsilosis ,C. metapsilosis , andC. fermentati. No resistant isolates were found by the CLSI method, whereas resistance rates of 1 to 2% were found by the EUCAST method. Overall, the EUCAST method resulted in MICs 1 to 2 dilutions higher than those found by the CLSI and Etest methods. The intra- and interlaboratory agreement between methods was >92%, except for the interlaboratory agreement between the EUCAST and CLSI methods (81%), where 17 to 31% of the differences were >2 2-fold dilutions forC. albicans ,C. glabrata ,C. tropicalis , and other rareCandida species and <6% forC. parapsilosis andC. krusei . For the other interlaboratory comparisons, the EUCAST method resulted in higher MICs than the Etest method for all species, but 2 2-fold dilutions. Overall, the CLSI method resulted in lower MICs than the Etest method, with 11% of all isolates demonstrating >2 2-fold-dilution differences (6 to 20% forC. albicans ,C. tropicalis , and rareCandida species; <5% forC. glabrata ,C. krusei , andC. parapsilosis ) and smaller differences found after 24 h. Despite these differences, categorical agreement was excellent (>97%), with only 1 to 2% very major errors between the EUCAST method and the other two methods.