Comparative activity of imipenem, ceftazidime and cefotaxime against Acinetobacter calcoaceticus

Imipenem was the most active drug against Acinetobacter, even against strains possessing beta-lactamases. MICs of imipenem for 50% and 90% of the A. calcoaceticus (var. anitratum) were 0.28 and 0.61 mg/l respectively whereas for ceftazidime they were 4.4 and 10.0, and for cefotaxime, 7.9 and 22.2 mg/l. No change occurred in the in-vitro activity of imipenem against Acinetobacter, during the period 1980-1985. Geometric mean MICs in 1985 were 0.33 mg/l for A. calcoaceticus var. anitratum; the values were lower for A. calcoaceticus var. lwoffi. Ceftazidime and cefotaxime MICs were also stable from 1981 to 1985, but the values were higher, geometric mean MICs being 5.3 and 10.1 mg/l respectively. MBCs of imipenem for A. calcoaceticus var. anitratum ranged from 0.194 to 0.35 mg/l; the ratio MBC/MIC was 1.17.