[Comparative in vitro study of the activity of 5 quinolones against Acinetobacter calcoaceticus]

The authors compared the in vitro activity of ofloxacin, pefloxacin, ciprofloxacin, norfloxacin and nalidixic acid against 143 clinical isolates of Acinetobacter calcoaceticus. Minimal inhibitory concentrations (MICs) were determined by the agar dilution method. Minimal bactericidal concentrations (MBCs) were measured using microplates. Ciprofloxacin, ofloxacin and pefloxacin were substantially active in vitro. MICs 50 were respectively 0.72, 0.69 and 1.05 micrograms/ml. Geometric means were 0.98, 1.03 and 1.64 micrograms/ml. Norfloxacin and nalidixic acid were slightly less active, with MICs 50 of 7.85 and 17.87 micrograms/ml and geometric means of 10.72 and 28.3 micrograms/ml respectively. Fifty percent of strains were killed by 1.5 micrograms/ml of pefloxacin; the greatest bactericidal in vitro activity was exhibited by ciprofloxacin whose MBC 50 was 0.60 micrograms/ml. Bactericidal activity of ofloxacin was comparable with a MBC 50 of 0.68 micrograms/ml. A significant difference was observed between the two varieties of Acinetobacter: Acinetobacter calcoaceticus var. Iwoffi was more susceptible to tested drugs than the anitratum variety. In short, new quinolone antimicrobial agents may be active in the treatment of nosocomial hospital infections due to Acinetobacter calcoaceticus which is one of the most resistant pathogens to currently available beta-lactams and aminoglycosides.