BACK MUTATIONS TO THE TEM-I BETA-LACTAMASE FROM TRC-1 LEAD TO RESTORED SENSITIVITY TO CLAVULANIC ACID

Back mutations from the TRC-1 beta-lactamase to the TEM-1 enzyme were selected in vitro. The revertant beta-lactamase was obtained from Esch erichia coli strain J62.2 carrying plasmid pUK901 which encodes the TR C-1 beta-lactamase. The revertant was obtained after repeated subcultu re of E. coli J62.2 (pUK901) in amoxycillin 512 mg/L for 5 days. The r evertant beta-lactamase had the same pI as TEM-1 (5.4) and had restore d inhibition by clavulanic acid (ID50 reduced from 4.2 mu M to 0.15 mu M). The prevalence of these beta-lactamases in the clinical populatio n may be the result of a two-way flux, with mutations in both forward and backward directions.