INVITRO ACTIVITIES OF CEFOPERAZONE AND SULBACTAM SINGLY AND IN COMBINATION AGAINST CEFOPERAZONE-RESISTANT MEMBERS OF THE FAMILY ENTEROBACTERIACEAE AND NONFERMENTERS

Among 28,000 isolates of the family Enterobacteriaceae and nonfermenters isolated at multiple medical centers, 1,084 (4%) were resistant to cefoperazone (MIC, ≥ 64 μg/ml) and 1,711 (6%) exhibited cefoperazone MICs of 2 to 32 μg/ml. Ninety-six percent of these 2,795 isolates produced β-lactamase, as determined by the nitrocefin test. Sulbactam alone (8 μg/ml) was inactive against 99.6% of the isolates other than Acinetobacter calcoaceticus and Pseudomonas cepacia. Sulbactam enhanced the activity of cefoperazone against 56% of the isolates of the family Enterobacteriaceae and 44% of the nonfermenters. In the presence of sulbactam concentrations of ≤ 8 μg/ml, 65% of the cefoperazone-resistant isolates had reductions in cefoperazone MICs of ≥ 2 log2 dilution steps and were susceptible to ≤ 32 μg/ml. Antagonism was not observed.