In vitro activity of modern penicillins and cephalosporins against enterococci

The in vitro activity of nine penicillin and cephalosporin antibiotics against enterococci was compared by MIC determination and killing curve experiments. To inhibit 90% of the 143 clinical isolates tested the following drug concentrations were required: mezlocillin, 1--2 micrograms/ml; azlocillin, 2 micrograms/ml; piperacillin, 4 micrograms/ml; cefazedone, 16 micrograms/ml; cefazolin and cefoperazone, 32 micrograms/ml; ticarcillin, 64 micrograms/ml. Cefotaxime and lamoxactam proved to be almost ineffective at 128 micrograms/ml which was the highest concentration tested. In killing curve experiments a reduction of viable cell count by 2--3 logs was achieved with all antibiotics except cefotaxime and lamoxactam. In general, the acylureido-penicillins exhibited a better bactericidal activity than the cephalosporins.