Selection of variants of the TEM-1 β lactamase, encoded by a plasmid of clinical origin, with increased resistance to β-lactamase inhibitors

A TEM-1 derived variant beta-lactamase with increased resistance to beta-lactamase inhibitors was selected in vitro. The variant beta-lactamase was obtained from the parent strain Escherichia coli J62-2 containing resistance plasmid R1 which encodes the TEM-1 beta-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 beta-lactamase with a clinically isolated TEM derived beta-lactamase, with increased resistance to beta-lactamase inhibitors, suggests that they are the same enzyme. Both beta-lactamases have the same pI at 5.25 and have similar ID50 values for the beta-lactamase inhibitors clavulanic acid, sulbactam and tazobactam.