Susceptibility of new beta-lactams to the expanded-spectrum beta-lactamase CTX-1.

Forty-three clinical isolates of enterobacteria were selected for the production of the new plasmid-mediated expanded-spectrum beta-lactamase CTX-1. The geometric means of MICs were ranged as follows: ticarcillin, greater than 4096 mg/l; ticarcillin + clavulanic acid (2 mg/l), 64-87 mg/l; LY 163892, 8.0-69.1 mg/l; cefotaxime, 5.7-26.4 mg/l; temocillin, 8.0-21.8 mg/l; Ro 158074, 4.0-18.7 mg/l aztreonam, 1.0-14.4 mg/l and BMY 28142, 1.4-2.8 mg/l. Moxalactam, imipenem and CM 40876 were resistant to hydrolysis and MICs were lower than 2.0 mg/l. A high protective effect on cefotaxime (MIC less than or equal to 0.5 mg/l) was obtained by sulbactam (4 mg/l). Escherichia coli transconjugants from each species showed similar levels of MICs.