COMPARISON OF A NEW COMMERCIAL COLORIMETRIC MICRODILUTION METHOD WITHA STANDARD METHOD FOR IN-VITRO SUSCEPTIBILITY TESTING OF CANDIDA SPP.AND CLYPTOCOCCUS NEOFORMANS

The Sensitive Yeast One method (AccuMed International Ltd, East Grinst ead, UK) is a microplate-based procedure that incorporates an oxidatio n-reduction indicator, Alamar Blue, for the in-vitro testing of five a ntifungal agents (amphotericin B, fluconazole, itraconazole, ketoconaz ole and flucytosine). We compared this colorimetric method with a stan dard broth microdilution test, performed according to US National Comm ittee for Clinical Laboratory Standards document M27-A guidelines, for determining the in-vitro susceptibilities of 180 isolates of Candida spp. (50 Candida albicans, 50 Candida glabrata, ten Candida kefyr, 20 Candida krusei, ten Candida lusitaniae, 20 Candida parapsilosis and 20 Candida tropicalis) and 20 isolates of Cryptococcus neoformans. The o verall agreement between the results of the two methods (colorimetric MICs within +/- two log(2) dilutions of standard MICs) were 99% for am photericin B, 96.5% for flucytosine, 93% for itraconazole, 91.5% for f luconazole and 85.5% for ketoconazole. The overall levels of agreement between the two methods were greater than or equal to 94% for six of the eight species tested, the exceptions being C. neoformans and C. tr opicalis where the overall agreement was 89% and 80% respectively. The poorest agreement between the results for individual agents was seen with C. tropicalis and the three azole agents (60-75% of colorimetric MICs within +/- two log(2) dilutions of standard MICs), and C. neoform ans for ketoconazole (50%). The Yeast One method appears to be a suita ble alternative procedure for routine antifungal susceptibility testin g of Candida spp. and C. neoformans.