MULTICENTER EVALUATION OF PROPOSED STANDARDIZED PROCEDURE FOR ANTIFUNGAL SUSCEPTIBILITY TESTING OF FILAMENTOUS FUNGI

A multicenter study was conducted to expand the generation and analysi s of data that supports the proposal of a reference method for the ant ifungal susceptibility testing of filamentous fungi. Broth microdiluti on MICs of amphotericin B and itraconazole were determined in 11 cente rs against 30 coded duplicate pairs of Aspergillus spp., Fusarium spp. , Pseudallescheria boydii, and Rhizopus arrhizus. The effect of inocul um density (approximately 10(3) and 10(4) CFU/ml), incubation time (24 , 48, and 72 h), and procedure of MIC determination (conventional and colorimetric [Alamar Blue] evaluation of growth inhibition) on intra- and interlaboratory agreement was analyzed. Based on intra- (97 to 100 %) and interlaboratory (94 to 95%) agreement for both drugs, the overa ll optimal testing conditions identified were determination of colorim etric MICs after 48 to 72 h of incubation with an inoculum density of approximately 10(4) CFU/ml. These testing conditions are proposed as g uidelines for a reference broth microdilution method.