title: Characterization of IMI-1 beta-lactamase, a class A carbapenem-hydrolyzing enzyme from Enterobacter cloacae.
abstract: In 1984, a year prior to the U.S. approval of imipenem for clinical use, a wound isolate and a bile isolate of Enterobacter cloacae were obtained from two patients in a California hospital. These isolates were resistant to imipenem, penicillins, and inhibitor combinations; early cephalosporins such as cephalothin, cefamandole, and cefoxitin; and cefoperazone. However, they were susceptible (MICs, < 4 micrograms/ml) to cefotaxime, ceftriaxone, ceftazidime, and moxalactam. Both strains produced an apparent TEM-1 beta-lactamase; an inducible NmcA-type imipenem-hydrolyzing beta-lactamase, IMI-1, with a pl of 7.05; and an inducible beta-lactamase with a pI of 8.1, typical of an E. cloacae AmpC beta-lactamase. Purified IMI-1 hydrolyzed imipenem and benzylpenicillin at modest rates, but more slowly than cephaloridine. The enzyme was inhibited by clavulanic acid and tazobactam. EDTA did not inhibit the cephaloridine-hydrolyzing activity. The beta-lactamase gene encoding IMI-1, imiA1, was cloned from E. cloacae 1413B. Sequence analysis identified the imiA1 gene as encoding a class A serine beta-lactamase. Both the imiA1 DNA and encoded amino acid sequences shared greater than 95% identity with the NmcA gene and its encoded protein. DNA sequence analysis also identified a gene upstream of imiA1 that shares > 95% identity with nmcR and that may encode a regulatory protein. In conclusion, IMI-1, a carbapenem-hydrolyzing beta-lactamase inhibited by clavulanic acid, was identified as a group 2f, class A, carbapenem-hydrolyzing cephalosporinase.
authors.affiliation: Wyeth Ayerst Research, Lederle Laboratories, New York 10965, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Rasmussen
authors.forename: K
authors.initials: K
authors.lastname: Bush
authors.forename: D
authors.initials: D
authors.lastname: Keeney
authors.forename: Y
authors.initials: Y
authors.lastname: Yang
authors.forename: R
authors.initials: R
authors.lastname: Hare
authors.forename: C
authors.initials: C
authors.lastname: O'Gara
authors.forename: A A
authors.initials: AA
authors.lastname: Medeiros
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000032:analysis; D004591:Electrophoresis, Polyacrylamide Gel; D016972:Enterobacter cloacae / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D007525:Isoelectric Focusing; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010957:Plasmids; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000032:analysis* / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases; C063912:carbapenemase