Molecular characterization of amoxicillin-clavulanate resistance in a clinical isolate of Escherichia coli.

The resistance phenotype of the clinical isolate of Escherichia coli 1941 was characterized by high-level resistance to penicillins and to combinations amoxicillin-ticarcillin/clavulanate and ampicillin/sulbactam. This resistance was carried by the conjugative plasmid pEC1941 that encoded a beta-lactamase activity. The purified enzyme focused at pI 5.