Post-β-lactamase-inhibitor effect of tazobactam in combination with ceftolozane on extended-spectrum-β-lactamase-producing strains

The post-β-lactamase-inhibitor effect (PBLIE) of tazobactam combined with ceftolozane was evaluated by time-kill assays on two clinical Escherichia coli strains producing CTX-M-15 with or without TEM-1. The organisms were exposed (2 h) to 4 μg/ml/4 μg/ml of ceftolozane-tazobactam (4× MIC), 4 μg/ml of ceftolozane, and medium containing no drug, washed, and resuspended in medium alone or medium containing ceftolozane-tazobactam or ceftolozane. The PBLIE was determined as 1.3 to 2.1 h, and a postantibiotic effect was measured as 0.8 to 0.9 h.