EVALUATION OF 80-PERCENT INHIBITION STANDARDS FOR THE DETERMINATION OF FLUCONAZOLE MINIMUM INHIBITORY CONCENTRATIONS IN 3 LABORATORIES

The purpose of this study was to evaluate 1:5 growth control dilutions (80% inhibition standards) to determine fluconazole minimum inhibitor y concentration (MIC) end points in three laboratories. We tested 39 s elected Candida species (in vitro susceptible: fluconazole MIC of less than or equal to 1 mu g/ml, and resistant: fluconazole MIC of greater than or equal to 8 mu g/ml) and Cryptococcus neoformans isolates by b roth macro- and microdilution procedures following the National Commit tee for Clinical Laboratory Standards proposed reference method for ye asts (M27-P). Macrodilution MIC(80)% were the lowest drug concentratio ns with turbidity (growth) less than or equal to that of specific 1:5 dilutions of the growth control. Microdilution MICs-2 were the lowest drug concentrations in which there was prominent decrease of growth. A total of 1608 MICs were evaluated. C. krusei, C. parapsilosis, and C. tropicalis strains had reproducible fluconazole MICs by both tests (2 4 and 48 h). Fluconazole MIC(80)% and MIC-2 end points were consistent at 24 h (with C. albicans) and move variable at 48 h. MICs of C. neof ormans were move reproducible at 72 h than at 48 h by both tests. This study suggests that the determination of fluconazole MICs is dependen t on the length of incubation and the yeast being tested, and that ant ifungal testing of the yeasts may be performed by either test.