In vitro activity of piperacillin and other microbials on 491 bacterial isolates.

We tested the activity of piperacillin against 491 bacterial local clinical isolates in comparison with ampicillin, mezlocillin, cefazolin, cefoperazone, cefotaxime, ceftazidime, moxalactam, and gentamicin, using an agar dilution technique and inocula of 10(6) and 10(4) colony forming units. The results confirmed the broad-spectrum activity of piperacillin against a wide range of bacterial pathogens. The activity against Pseudomonas aeruginosa was encouraging, and it was one of the most active agents tested against that species. Its lack of stability for certain types of beta-lactamases was manifested by large differences in the minimal inhibitory concentration (MIC) activity between inocula of 10(6) and 10(4), and by the high MIC to inhibit 90% of strain of certain species compared with the MIC to inhibit 50% of strain. The activity of piperacillin suggests its clinical evaluation for use in combination with other agents in serious sepsis, in situations where beta-lactamase-producing strains are rare, and in antipseudomonal therapy.