Multicenter studies of tigecycline disk diffusion susceptibility results for Acinetobacter spp.

Acinetobacter sp. isolates having multidrug resistance (MDR) patterns have become common in many medical centers worldwide, limiting therapeutic options. A five-center study tested 103 contemporary clinical Acinetobacter spp., including MDR strains, by reference broth microdilution and disk diffusion (15-mu g disk content) methods against tigecycline. Applying U.S. Food and Drug Administration tigecycline breakpoint criteria for Enterobacteriaceae (susceptibility at <= 2 mu g/ml [<= 1 mu g/ml by the European Committee on Antimicrobial Susceptibility Testing]; disk diffusion breakpoints at >= 19 mm and <= 14 mm) to Acinetobacter spp. led to an unacceptable error rate (23.3%). However, an adjustment of tigecycline disk diffusion breakpoints (susceptible/resistant) to >= 16/<= 12 mm reduced intermethod errors to an acceptable level (only 9.7%, all minor).