COMPARISON OF ANTIBACTERIAL ACTIVITIES OF MEROPENEM AND 6 OTHER ANTIMICROBIALS AGAINST PSEUDOMONAS-AERUGINOSA ISOLATES FROM NORTH-AMERICAN STUDIES AND CLINICAL-TRIALS

The in vitro activity of meropenem was compared with those of six othe r antimicrobials against up to 1,182 clinical isolates of Pseudomonas aeruginosa from 16 North American centers by means of standardized con trolled methods. Meropenem was the most active drug. These isolates we re less frequently resistant to meropenem (4.2%) than to imipenem (12. 5%), ceftazidime (15.6%), piperacillin (21%), ciprofloxacin (16%), tob ramycin (26%), or gentamicin (29.8%). Of 147 imipenem-resistant P. aer uginosa isolates, 43.8% were susceptible to meropenem, and 26.9% addit ional isolates were moderately susceptible to meropenem. Of 49 meropen em-resistant (MIC, greater than or equal to 16 mu g/mL) isolates, 85.7 % were also imipenem-resistant, and 24% to 79% were resistant to other antimicrobials. Meropenem MICs were lower than imipenem and ceftazidi me MICs for 92 P. aeruginosa isolates from meropenem clinical trials. Carbapenem MICs of greater than or equal to 16 mu g/mL for selected P, aeruginosa isolates from meropenem clinical trials were associated wi th loss of the similar to 45-kD outer-membrane protein and/or producti on of type I beta-lactamases. No metallo-beta-lactamases (e.g., ''effi cient'' carbapenemases) were detected.