COMPARATIVE-EVALUATION OF MACRODILUTION AND ALAMAR COLORIMETRIC MICRODILUTION BROTH METHODS FOR ANTIFUNGAL SUSCEPTIBILITY TESTING OF YEAST ISOLATES

A comparative evaluation of the macrodilution method and the Alamar co lorimetric method for the susceptibility testing of amphotericin B, fl uconazole, and flucytosine was conducted with 134 pathogenic yeasts, T he clinical isolates included 28 Candida albicans, 17 Candida tropical is, 15 Candida parapsilosis, 12 Candida krusei, 10 Candida lusitaniae, 9 Candida guilliermondii, 18 Torulopsis glabrata, and 25 Cryptococcus neoformans isolates. The macrodilution method was performed and inter preted according to the recommendations of the National Committee for Clinical Laboratory Standards (document M27-P), and the Alamar colorim etric method was performed according to the manufacturer's instruction s. For the Alamar colorimetric method, MICs mere determined at 24 and 48 h of incubation for Candida species and T. glabrata and at 48 and 7 2 h of incubation for C. neoformans. The overall agreement within +/- 1 dilution for Candida species and T. glabrata against the three antif ungal agents was generally good, with the values for amphotericin B, f luconazole, and flucytosine being 85.3, 77.9, and 86.2%, respectively, at the 24-h readings and 69.3, 65.2, and 97.2%, respectively, at the 48-h readings, Most disagreement was noted with fluconazole against C. tropicalis and T. glabrata. Our studies indicate that determination o f MICs at 24 h by the Alamar colorimetric method is a valid alternate method for testing amphotericin B, fluconazole, and flucytosine agains t Candida species but not for testing fluconazole against C. tropicali s and T. glabrata. For flucytosine, much better agreement can be demon strated against Candida species and T. glabrata at the 48-h readings b y the Alamar method, Excellent agreement within +/- 1 dilution can als o be observed for amphotericin B, fluconazole, and flucytosine (80, 96 , and 96%, respectively) against C, neoformans when the MICs were dete rmined at 72 h by the Alamar method.