Biochemical characterization of the carbapenem-hydrolyzing β-lactamase AsbM1 fromAeromonas sobriaAER 14M: a member of a novel subgroup of metallo-β-lactamases

AsbM1, a carbapenem-hydrolyzing beta-lactamase produced by Aeromonas sobria AER 14M, was purified chromatographically, with anion exchange chromatography performed in the absence of Zn2+. The molecular mass of AsbM1 was approximately 34,000; the isoelectric point was 9.1. AsbM1 had high hydrolytic specificity for carbapenems but low hydrolysis rates for penicillins and cephalosporins. AsbM1 was resistant to the commercially available beta-lactamase inhibitors but was inhibited by pCMB and the chelators EDTA and o-phenanthroline. Zinc, an activator for many metallo-beta-lactamases, inhibited AsbM1 with an IC50 of 8 microM. Analysis of the N-terminal sequence (27 amino acids) showed 26% similarity to the CphA metallo-beta-lactamase. Because of the high specificity for carbapenems and the sensitivity to inhibition by Zn2+, AsbM1 should be included in a new subgroup of metallo-beta-lactamases.