[Investigation of susceptibility testing methods for micafungin: comparison of two microdilution methods]

As there is not yet a standardized in vitro susceptibility test of micafungin (MCFG), we evaluated the methods of such testing, focusing on the judgment method of MIC, based on the National Committee for Clinical Laboratory Standards (NCCLS) M27-A2, M38-A, the proposed standards of The Japanese Society for Medical Mycology (JSMM) for yeast (JSMM-Y) and for filamentous fungi (JSMM-F) against Candida spp. and Aspergillus spp. The judgment of MIC value was performed spectrophotometrically and visually in both (NCCLS and JSMM) assays. Only the spectrophotometric MIC judgment against Aspergillus spp. in the NCCLS assay used two end points: 80% inhibitory concentration (IC80) of the growth control and 50% inhibitory concentration (IC50). The end point for the visual judgment against Aspergillus spp. in the NCCLS assay was determined to be no growth from the small clumps of altered hyphae in the microtiter plate. The other MIC judgments used an IC80 end point. The MICs of MCFG for Candida spp. were 4mug/ml and 0.0078-0.0313mug/ml). However, the MICs using the IC50 end point and those by JSMM assay agreed with the result of the visual assessment. Therefore, we recommend the JSMM assay, the NCCLS assay using the IC50 end point or the novel visual judgment for the susceptibility testing of MCFG against Aspergillus spp.