COMPARATIVE-STUDY OF BROTH MACRODILUTION AND MICRODILUTION TECHNIQUESFOR IN-VITRO ANTIFUNGAL SUSCEPTIBILITY TESTING OF YEASTS BY USING THETIONAL-COMMITTEE-FOR-CLINICAL-LABORATORY-STANDARDS PROPOSED STANDARD

A comparative study of broth macro- and microdilution methods for susc eptibility testing of fluconazole, itraconazole, flucytosine, and amph otericin B was conducted with 273 yeasts. The clinical isolates includ ed 100 Candida albicans, 28 Candida tropicalis, 25 Candida parapsilosi s, 15 Candida lusitaniae, 15 Candida krusei, 50 Cryptococcus neoforman s var. neoformans, 25 Torulopsis (Candida) glabrata, and 15 Trichospor on beigelii strains. Both methods were performed according to the Nati onal Committee for Clinical Laboratory Standards' (NCCLS) recommendati ons (document M27-P). For fluconazole, itraconazole, and flucytosine, the endpoint was the tube that showed 80% growth inhibition compared,v ith the growth control for the macrodilution method and the well with slightly hazy turbidity (score I) compared with the growth control for the microdilution method. For amphotericin B, the endpoint was the tu be and/or well in which there was absence of growth. For the reference macrodilution method, the MICs were determined after 48 h of incubati on for Candida spp., T. glabrata, and T. beigelii and after 72 h for C . neoformans var. neoformans. For the microdilution method, either the first-day MICs (24 h for all isolates other than C. neoformans var. n eoformans and 48 h for C. neoformans var. neoformans) or the second-da y MICs (48 and 72 h, respectively) were evaluated. The agreement withi n one doubling dilution of the macrodilution reference for all drugs,v as higher with the second-day MICs than with the first-day MICs for th e microdilution test for most of the tested strains. General agreement was 92% for fluconazole, 85.7% for itraconazole, 98.3% for flucytosin e, and 96.4% for amphotericin B. For C. neoformans var. neoformans and T. beigelii, the agreement of the first-day reading was higher than t hat of the second-day reading for fluconazole (94 versus 92%, respecti vely, for C. neoformans var. neoformans, and 86.7 versus 80%, respecti vely, for T. beigelii). Our studies indicate that the microdilution te chnique performed following the NCCLS guidelines with a second-day rea ding is a valid alternative method for testing fluconazole, itraconazo le, flucytosine, and amphotericin B against these eight species of yea sts.