title: Inhibitor-sensitive AmpC beta-lactamase variant produced by an Escherichia coli clinical isolate resistant to oxyiminocephalosporins and cephamycins.
abstract: Escherichia coli HKY28, a ceftazidime-resistant strain isolated from a urine specimen in Japan, produced an inhibitor-sensitive AmpC beta-lactamase variant. The deduced amino acid sequence of the enzyme contained a number of substitutions and a tripeptide deletion (Gly286-Ser287-Asp288) compared with the sequence of native AmpC of E. coli. When the deletion was reverted by a 9-base insertion at the relevant site of ampC in the clone, the typical inhibitor-resistant phenotype of AmpC was restored, while at the same time the levels of resistance to ceftazidime, cefpirome, and cefepime were reduced eightfold or more. Molecular modeling studies indicated that a structural change took place in the H-10 helix as a result of the deletion, and this change caused an alteration of the substrate binding site, leading to a unique phenotype analogous to that of inhibitor-sensitive class A extended-spectrum beta-lactamases. The degree of inhibition was greater with sulbactam and tazobactam than with clavulanic acid. To our knowledge, this is the first report to have characterized an E. coli ampC that encodes chromosomal AmpC beta-lactamase sensitive to the available beta-lactamase inhibitors.
authors.affiliation: Department of Bacterial Pathogenesis and Infection Control, National Institute of Infectious Diseases, 4-7-1 Gakuen, Musashi-Murayama, Tokyo 208-0011, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Doi
authors.forename: Jun-ichi
authors.initials: J
authors.lastname: Wachino
authors.forename: Masaji
authors.initials: M
authors.lastname: Ishiguro
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kurokawa
authors.forename: Kunikazu
authors.initials: K
authors.lastname: Yamane
authors.forename: Naohiro
authors.initials: N
authors.lastname: Shibata
authors.forename: Keigo
authors.initials: K
authors.lastname: Shibayama
authors.forename: Keiko
authors.initials: K
authors.lastname: Yokoyama
authors.forename: Haru
authors.initials: H
authors.lastname: Kato
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Yagi
authors.forename: Yoshichika
authors.initials: Y
authors.lastname: Arakawa
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics*; D002442:Ceftazidime / Q000494:pharmacology; D018550:Cephalosporin Resistance; D002511:Cephalosporins / Q000494:pharmacology*; D002513:Cephamycins / Q000494:pharmacology*; D003001:Cloning, Molecular; D003470:Culture Media; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D004927:Escherichia coli Infections / Q000201:enzymology / Q000382:microbiology*; D017353:Gene Deletion; D022761:Gene Transfer, Horizontal; D007525:Isoelectric Focusing; D008826:Microbial Sensitivity Tests; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013379:Substrate Specificity; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D002511:Cephalosporins; D002513:Cephamycins; D003470:Culture Media; D004791:Enzyme Inhibitors; D065093:beta-Lactamase Inhibitors; D002442:Ceftazidime; C048795:AmpC beta-lactamases; D001618:beta-Lactamases