SELECTION OF CANDIDATE QUALITY-CONTROL ISOLATES AND TENTATIVE QUALITY-CONTROL RANGES FOR IN-VITRO SUSCEPTIBILITY TESTING OF YEAST ISOLATES BY NATIONAL COMMITTEE FOR CLINICAL LABORATORY STANDARDS PROPOSED STANDARD METHODS

The National Committee for Clinical Laboratory Standards has developed a proposed standard method for in vitro antifungal susceptibility tes ting of yeast isolates (National Committee for Clinical Laboratory Sta ndards, document M27-P, 1992). In order for antifungal testing by the M27-P method to be accepted, reliable quality control (QC) performance criteria must be developed. In the present study, five laboratories t ested 10 candidate QC strains 20 times each against three antifungal a gents: amphotericin B, fluconazole, and 5-fluorocytosine. All sites co nformed to the M27-P standards and used a common lot of tube dilution reagents and RPMI 1640 broth medium. Overall, 98% of MIC results with amphotericin B, 95% with fluconazole, and 92% with 5-fluorocytosine fe ll within the desired 3-log(2) dilution range (mode +/- 1 log(2) dilut ion). Excellent performance with all three antifungal agents was obser ved for six strains: Candida albicans ATCC 90028, Candida parapsilosis ATCC 90018, C. parapsilosis ATCC 22019, Candida krusei ATCC 6258, Can dida tropicalis ATCC 750, and Saccharomyces cerevisiae ATCC 9763. With these strains, 3-log, dilution ranges encompassing 94 to 100% of MICs for all three drugs were established. Additional studies with multipl e lots of RPMI 1640 test medium will be required to establish definiti ve QC ranges.