In vitro activity of fleroxacin and 6 other antimicrobials against Acinetobacter anitratus.

The in vitro activity of the 4-quinolone compound fleroxacin (Ro-23-6240) was compared with that of enoxacin, ofloxacin, cefepime (BMY-28142), ceftazidime, ceftriaxone, and tobramycin against a total of 30 recent clinical isolates of Acinetobacter calcoaceticus subsp. anitratum. Susceptibility testing (MIC50/MIC90) was performed by a microtiter broth dilution method and the combination effect of ceftriaxone plus tobramycin was studied by checkerboard titration in microtiter trays. Fleroxacin inhibited most A. calcoaceticus subsp. anitratum at 1 microgram/ml and was as active as enoxacin or tobramycin but slightly less active than ofloxacin (MIC50 = 0.25 microgram/ml; MIC90 = 2.5 microgram/ml) or cefepime (BMY-28142: MIC50 = 0.25 microgram/ml; MIC90 = 1 microgram/ml). Ceftazidime and ceftriaxone were inactive (MIC90 = 8 micrograms/ml and 32 micrograms/ml, respectively). The combination of ceftriaxone plus tobramycin was synergistic in 16.7%, additive in 60%, and indifferent in 23.3%.