Comparative evaluation of MIC values of <i>Trichosporon</i> spp. by MTT assay and CLSI M27-A3 broth microdilution reference methods

Objectives: The objective of this study was to determine and compare the minimum inhibitory concentration (MIC) values of Trichosporon spp. by MTT (3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl- 2H-tetrazoliumbromide) assay, and Clinical and Laboratory Standards Institute M27-3 rd edition (CLSI M27-A3) broth microdilution methods. Materials and Methods: Antifungal susceptibility testing was done by CLSI M27-A3 broth microdilution and MTT assay for all the 72 Trichosporon isolates after genus specific and Trichosporon asahii specific polymerase chain reaction (PCR). Candida krusei ATCC 6258 was used as the reference strain. Statistical analysis: All statistical data were analyzed using the Statistical Package for the Social Sciences, version 17 for Microsoft Windows. The percentage of agreement was calculated using the Type C intraclass correlation coefficient. Results: The MICs by MTT assay strongly correlated with those obtained by CLSI M27-A3 method, by being either the same or within 1 dilution of MIC by CLSI method. Furthermore, the ranges of MICs obtained by MTT and CLSI method were all identical in our study. The overall agreement between the two methods for the Trichosporon isolates was good, that is, 90.8% in our study. Conclusions: MTT assay can be an alternative method that assists reading of MICs visually with a colored end point, making it easier compared to CLSI M27-A3 method. MTT assay can also be standardized for other yeasts and molds so that antifungal susceptibility tests can be done for different fungi.