in contrast with ampicillin and piperacillin , the two carbapenems and three cephalosporins tested showed no reduction in activity against beta-lactamase producing isolates . beta-lactam concentrations required for inhibition of 50 % and 90 % of beta-lactamase negative isolates with reduced susceptibility to ampicillin ( mic greater than or equal to 1 mg/l ) were increased in comparison with similar concentrations required for the ampicillin-susceptible group .
C0031955
piperacillin
C0002680
ampicillin