Antibacterial properties of imipenem with special reference to the activity against methicillin-resistant staphylococci, cefotaxime-resistant Enterobacteriaceae and Pseudomonas aeruginosa.

Imipenem was examined with standardized agar dilution procedures against a wide range of bacteria. Geometric mean MICs against the genera Escherichia, Klebsiella, Enterobacter, Citrobacter and Serratia were 0.1-0.4 mg/l, and Proteus and Providencia spp. were inhibited by 0.25-4 mg/l. Acinetobacter calcoaceticus var. anitratum strains were inhibited by concentrations ranging from 0.12-0.5 mg/l. Methicillin-susceptible staphylococci were highly susceptible to the drug (MICs: less than or equal to 0.03 mg/l) and enterococci were inhibited by 0.25-16 mg/l. Most of the multi-resistant JK corynebacteria were resistant to imipenem. Imipenem was more active than any other beta-lactam against methicillin-resistant staphylococci; this was also demonstrated in a population analysis. Imipenem-resistant minorities in populations, however, were also observed. Cefotaxime-resistant and -intermediate Enterobacter and Citrobacter strains were inhibited by concentrations of 0.5 mg/l or less. No third-generation cephalosporin nor any other beta-lactam showed similarly high activity against these groups of organisms. Among 20 ceftazidime-resistant and 20 ceftazidime-susceptible isolates of Pseudomonas aeruginosa, no strain was resistant and only five ceftazidime-resistant strains were intermediately susceptible (MIC, 8 mg/l) to imipenem.