Characterization of a novel AmpC β-lactamase produced by a carbapenem-resistant Cedecea davisae clinical isolate.

A Cedecea davisae isolate, which was intermediate or resistant to third-generation cephalosporins and carbapenems, was recovered from a urine sample. Susceptibility testing, isoelectric focusing, and analysis of outer membrane proteins showed that AmpC β-lactamase expression combined with porin deficiency accounted for the carbapenem resistance. A cloning experiment followed by phenotypic and enzymatic characterization identified a novel class C enzyme that was phylogenetically and biochemically close to the chromosome-borne β-lactamases of the genera Enterobacter and Citrobacter.