Tazobactam is a potent inactivator of selected inhibitor-resistant class A β-lactamases

The beta-lactam beta-lactamase inhibitor combinations (ampicillin/clavulanate, ampicillin/sulbactam, ticarcillin/clavulanate and piperacillin/tazobactam) were tested against selected inhibitor-resistant class A beta-lactamases of the TEM and OHIO-1 varieties. Minimum inhibitor concentrations (MIC) revealed that the Escherichia coli DH5 alpha transconjugate strains that possessed the OHIO-1 beta-lactamase, Met69Ile mutant of the OHIO-1 beta-lactamase, TEM-30 (Arg244Ser) and TEM-31 (Arg244Cys) beta-lactamase were most susceptible to piperacillin and piperacillin/tazobactam. Kinetic experiments with each beta-lactamase demonstrated that tazobactam was 10-25-fold more potent than clavulanate or sulbactam against TEM-30 and TEM-31 beta-lactamase. Tazobactam was also as effective as clavulanate against the Met69Ile mutant of the OHIO-1 beta-lactamase. Among the clinically available beta-lactams and beta-lactamase inhibitors, piperacillin/tazobactam appears to be the most potent combination against selected inhibitor-resistant strains of TEM and OHIO-1 beta-lactamase.