Contribution of extended-spectrum AmpC (ESAC) beta-lactamases to carbapenem resistance in Escherichia coli.

ESAC beta-lactamases have increased catalytic efficiencies toward extended-spectrum cephalosporins and to a lesser extent toward imipenem as compared with the wild-type cephalosporinases. We show here that ESAC expression associated with the loss of both OmpC and OmpF porins conferred in Escherichia coli a high level of resistance to ertapenem and reduced the susceptibility to imipenem. On the contrary, ESAC expressed in the OmpC- or OmpF-deficient E.

Molecular characterization of AmpC-producing Escherichia coli clinical isolates recovered in a French hospital.

Objectives: To characterize the AmpC-type beta-lactamases produced by Escherichia coli clinical isolates.

Methods: E. coli isolates recovered in a French hospital in 2006 were selected on the basis of a resistance phenotype consistent with increased AmpC production.