In vitro activity of Gemifloxacin against contemporary clinical bacterial isolates from eleven North American medical centers, and assessment of disk diffusion test interpretive criteria

A total of 5499 contemporary clinical bacterial isolates were tested for susceptibility to gemifloxacin and four comparison agents by the broth microdilution method. Gemifloxacin activity against Enterobacteriaceae was generally comparable to that of ciprofloxacin and trovafloxacin, but because the gemifloxacin susceptible MIC breakpoint is lower, the percent susceptible to gemifloxacin was less than that to the other quinolones for some species. All agents were less active against Pseudomonas spp. Gemifloxacin was the most active agent tested against Gram-positive species, though Corynebacterium jeikeium and vancomycin-resistant enterococci were uniformly resistant to all agents tested. With staphylococci, a bimodal distribution of gemifloxacin MICs corresponded with susceptibility or resistance to ciprofloxacin. The significance of ciprofloxacin-resistant staphylococci that have susceptible gemifloxacin MICs is not known at this time. Disk diffusion tests were performed simultaneously with gemifloxacin and trovafloxacin as a control drug. Gemifloxacin MIC-zone diameter scattergrams indicated that interpretive discrepancy rates based on previously proposed criteria when using less than or equal to0.5 mug/ml as the susceptible MIC breakpoint was within acceptable limits. However, with the currently proposed MIC breakpoint of less than or equal to0.25 mug/ml, tentative zone diameter breakpoints of greater than or equal to 22 mm for susceptible, 19-21 mm for intermediate and less than or equal to 18 mm for resistant are proposed. (C) 2000 Elsevier Science Inc. All rights reserved.