COMPARATIVE AND COLLABORATIVE EVALUATION OF STANDARDIZATION OF ANTIFUNGAL SUSCEPTIBILITY TESTING FOR FILAMENTOUS FUNGI

The purpose of the study was to evaluate the interlaboratory agreement of broth dilution susceptibility methods for five species of conidium -forming (size range, 2 to 7 mu m) filamentous fungi. The methods used included both macro- and microdilution methods that were adaptations of the proposed reference method of the National Committee for Clinica l Laboratory Standards for yeasts (m27-P). The MICs of amphotericin B, fluconazole, itraconazole, miconazole, and ketoconazole were determin ed in six centers by both macro- and microdilution tests for 25 isolat es of Aspergillus flavus, Aspergillus fumigatus, Pseudallescheria boyd ii, Rhizopus arrhizus, and Sporothrix schenckii. All isolates produced clearly detectable growth within 1 to 4 days at 35 degrees C in the R PMI 1640 medium. Colony counts of 0.4 x 10(6) to 3.3 x 106 CFU/ml (mea n, 1.4 x 10(6) CFU/ml) were demonstrated in 90% of the 148 inoculum pr eparations. Overall, good intralaboratory agreement was demonstrated w ith amphotericin B, fluconazole, and ketoconazole MICs (90 to 97%). Th e agreement was lower with itraconazole MICs (59 to 79% median). Inter laboratory reproducibility demonstrated similar results: 90 to 100% ag reement with amphotericin B, fluconazole, miconazole, and ketoconazole MICs and 59 to 98% with itraconazole MICs. Among the species tested, the MICs for S. schenckii showed the highest variability. The results of the study imply that it may be possible to develop a reference meth od for antifungal susceptibility testing of filamentous fungi.