Activities of piperacillin, ceftazidime, cefepime and cefpirome against Pseudomonas aeruginosa strains with intrinsic ticarcillin resistance.

The in vitro activities of cefepime and cefpirome against 44 intrinsically ticarcillin-resistant strains of Pseudomonas aeruginosa were compared to their activities against 20 ticarcillin-susceptible strains by MIC determination and the disk test. Time-killing curves were constructed for piperacillin, ceftazidime, cefepime and cefpirome against two susceptible and two resistant strains. The activities of cefepime and cefpirome against the resistant strains were impaired, and most of the strains were of intermediate sensitivity to these agents. The time-killing curves of the four beta-lactams were similar, with a modest decline in viable cell counts over the first 6 h followed by regrowth. There was no difference between the susceptible and resistant strains.