Dissemination of the novel plasmid-mediated beta-lactamase CTX-1, which confers resistance to broad-spectrum cephalosporins, and its inhibition by beta-lactamase inhibitors.

The novel beta-lactamase CTX-1 (pI 6.3) encoded on a transferable 84-kilobase plasmid was found in six different bacterial species. It was responsible for a significant decrease in susceptibility towards most penicillins and cephalosporins, except imipenem, temocillin, and cephalosporins which have a 7-alpha-methoxy substituent. Synergy between either ampicillin, piperacillin, cefotaxime, ceftazidime, or aztreonam and three beta-lactamase inhibitors (clavulanic acid, sulbactam, and YTR 830) was generally found for different strains harboring CTX-1. This enzyme may be related to or derived from the TEM enzyme, since an intragenic probe of the TEM-1 gene hybridized with a fragment of the plasmid carrying CTX-1.