Inhibitor-sensitive AmpC beta-lactamase variant produced by an Escherichia coli clinical isolate resistant to oxyiminocephalosporins and cephamycins.
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.
Doi
Yohei
Y
Department of Bacterial Pathogenesis and Infection Control, National Institute of Infectious Diseases, 4-7-1 Gakuen, Musashi-Murayama, Tokyo 208-0011, Japan.
Wachino
Jun-ichi
J
Ishiguro
Masaji
M
Kurokawa
Hiroshi
H
Yamane
Kunikazu
K
Shibata
Naohiro
N
Shibayama
Keigo
K
Yokoyama
Keiko
K
Kato
Haru
H
Yagi
Tetsuya
T
Arakawa
Yoshichika
Y
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*
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