Superior effect of tazobactam/piperacillin compared to piperacillin on beta-lactamase-producing Pseudomonas aeruginosa.

To evaluate the synergistic antimicrobial effects of tazobactam (TAZ), a beta-lactamase inhibitor, and piperacillin (PIPC) on Pseudomonas aeruginosa, we compared the antimicrobial effects of TAZ/PIPC with those of PIPC alone on bacteria inducibly or constitutively producing beta-lactamase. TAZ/PIPC had more potent antimicrobial effects compared with PIPC on clinical isolates producing beta-lactamase. In the treatment of mouse systemic infection, the therapeutic effect of PIPC was markedly decreased by beta-lactamase, but that of TAZ/PIPC was only slightly decreased. In the treatment of local infections in mice, the therapeutic effects of PIPC were decreased due to the induction of beta-lactamase and the emergence of bacterial strains constitutively producing beta-lactamase, while those of TAZ/ PIPC were not affected.