Comparison of four reading methods of broth microdilution based on the clinical and laboratory standards institute...

This study aimed to compare the susceptibilities of 5 reference strains and 28 isolates of Candida spp., to micafungin, amphotericin B, flucytosine, fluconazole, itraconazole, voriconazole, and miconazole, obtained by visually determined minimum inhibitory concentration (MIC) using the agitation method (V-A), as described in the Clinical and Laboratory Standards Institute M27-A3 document; visual determinations without agitation (V-NA); and spectrophotometric determinations for the presence or absence of agitation (SP-A and SP-NA, respectively). Our results indicate that when the V-NA, SP-A, and SP-NA-the 3 alternative microdilution procedures for MIC endpoint determinations-were compared with the V-A, excellent agreements were observed between the V-NA and V-A rather than with the spectrophotometric methods (between the SP-A or SP-NA, and V-A). Furthermore, many errors occurred while using the SP-A method in the presence of agitation and some isolates showed major errors. Three of 5 isolates that showed very major errors between the spectrophotometric SP-A or SP-NA, and the reference V-A method were trailing isolates. Therefore, it was suggested that the MICs of Candida spp. obtained by the V-NA method were more precise than those by the conventional SP-A method.