Piperacillin with and without tazobactam against extended-spectrum beta-lactamase-producing Pseudomonas aeruginosa in a rat thigh abscess model

Background: We compared the antibacterial effect of piperacillin, piperacil lin-tazobactam and imipenem in a paired rat thigh abscess model. Methods: T wo abscesses were provoked in the thighs of rats, one on the right with an extended-spectrum beta-lactamase (OXA-14)-producing Pseudomonas nosa (Ps-16 2) and the other on the left thigh with a control strain. Results: The colo ny counts from the abscesses in log 10 colony-forming units per gram (mean +/- SD) in the imipenem group were 2.78 +/- 1.71 and 3.19 +/- 1.66, in the piperacillin-tazobactam group 4.36 +/- 0.23 and 2.44 +/- 1.97, and in the p iperacillin group 4.44 +/- 0.21 and 3.71 +/- 0.99 for Ps-162 and the contro l strain, respectively. The mean colony counts were different (p < 0.05) be tween Ps-162 and the control strain in the piperacillin and piperacillin-ta zobactam groups. Conclusion: These data showed that piperacillin and pipera cillin-tazobactam were significantly less effective against extended-spectr um beta-lactamase-producing P. aeruginosa, while imipenem was equally effec tive against both Ps-162 and the control strain in this abscess model. Copy right (C) 2001 S. Karger AG, Basel.