SELECTION OF VARIANTS OF THE TEM-1 BETA-LACTAMASE, ENCODED BY A PLASMID OF CLINICAL-ORIGIN, WITH INCREASED RESISTANCE TO BETA-LACTAMASE INHIBITORS

A TEM-1 derived variant β lactamase with increased resistance to β lactamase inhibitors was selected in vitro. The variant β lactamase was obtained from the parent strain Escherichia coli J62-2 containing resistance plasmid R1 which encodes the TEM-1 β lactamase. The variants were obtained by repeated subculture of E. coli J62-2 (R1) for five days in the presence of sub-inhibitory concentrations of amoxycillin plus clavulanic acid. Comparison of this variant β lactamase with a clinically isolated TEM derived β lactamase, with increased resistance to β lactamase inhibitors, suggests that they are the same enzyme. Both β lactamases have the same pI at 5·25 and have similar ID50 values for the β lactamase inhibitors clavulanic acid, sulbactam and tazobactam. © 1993 The British Society for Antimicrobial Chemotherapy.