CHARACTERIZATION OF A NEW TEM-TYPE BETA-LACTAMASE RESISTANT TO CLAVULANATE, SULBACTAM, AND TAZOBACTAM IN A CLINICAL ISOLATE OF ESCHERICHIA-COLI

A clinical Escherichia coli strain highly resistant to the combination s of amoxicillin-clavulanate, ampicillin-sulbactam, and piperacillin-t azobactam was isolated from a patient with a community-acquired urinar y tract infection who was previously treated with amoxicillin-clavulan ate. These resistances were carried by a 45-kb conjugative plasmid enc oding for a single beta-lactamase with a pl of 5.4. Cloning and sequen cing of the new beta-lactamase, IRT-3, revealed identity with the blaT 1 gene encoding the TEM-1 beta-lactamase except for a replacement of t he methionine residue at position 67 by isoleucine and of the methioni ne residue at position 180 by threonine. Both mutations were segregate d by the construction of hybrid genes, and only the mutation at methio nine at position 67 was related to resistance to the suicide inhibitor s. The inhibitory effects of clavulanate, sulbactam, and tazobactam on the TEM-1 enzyme were substantially decreased in comparison with thos e on IRT-3, as indicated by the 50% inhibitory Concentrations.