title: A novel ceftazidime-hydrolysing extended-spectrum beta-lactamase, CTX-M-54, with a single amino acid substitution at position 167 in the omega loop.
abstract: OBJECTIVE
  To characterize a novel ceftazidime-hydrolysing CTX-M mutant, designated CTX-M-54, produced by Klebsiella pneumoniae clinical isolate BDK0419 and to investigate its genetic environment.
  
  
  METHODS
  Antimicrobial susceptibilities were determined by disc diffusion and agar dilution methods, and the double-disc synergy test was carried out. Detection of genes encoding class A beta-lactamases was performed by PCR amplification, and the genetic organization of the blaCTX-M-54 gene was investigated by PCR and sequencing of the regions surrounding this gene. Kinetic parameters were determined from purified CTX-M-54.
  
  
  RESULTS
  The strain BDK0419 contained a transferable plasmid with a molecular size of approximately 21 kbp that carries both blaSHV-2a and blaCTX-M-54 beta-lactamase genes, along with two other plasmids. The blaCTX-M-54 gene was flanked upstream by an ISEcp1 insertion sequence and downstream by an IS903-like element. CTX-M-54 had a P167Q substitution within the omega loop region of class A beta-lactamases compared with the sequence of CTX-M-3. The MIC of ceftazidime for K. pneumoniae BDK0419 was 16-fold higher than that of cefotaxime; however, the kinetic parameter of CTX-M-54 against ceftazidime revealed a low catalytic efficiency.
  
  
  CONCLUSIONS
  This work shows once again that novel CTX-M enzymes with an expanded activity towards ceftazidime through a single amino acid substitution can be identified from clinical isolates. Thus, detection of CTX-M enzymes can no longer be based solely on the resistance phenotypes of clinical isolates towards ceftazidime and cefotaxime.
authors.affiliation: Department of Laboratory Medicine, Kosin University College of Medicine 602-030, 34 Amnam-Dong, Suh-Gu, Busan, Korea.
authors.forename: Il Kwon
authors.initials: IK
authors.lastname: Bae
authors.forename: Byung Ho
authors.initials: BH
authors.lastname: Lee
authors.forename: Hyun Yong
authors.initials: HY
authors.lastname: Hwang
authors.forename: Seok Hoon
authors.initials: SH
authors.lastname: Jeong
authors.forename: Seong Geun
authors.initials: SG
authors.lastname: Hong
authors.forename: Chulhun L
authors.initials: CL
authors.lastname: Chang
authors.forename: Hyo-Sun
authors.initials: HS
authors.lastname: Kwak
authors.forename: Hyoung Jin
authors.initials: HJ
authors.lastname: Kim
authors.forename: Hasik
authors.initials: H
authors.lastname: Youn
mesh_terms: D019943:Amino Acid Substitution; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001483:Base Sequence; D002442:Ceftazidime / Q000378:metabolism* / Q000494:pharmacology; D004251:DNA Transposable Elements / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D005260:Female; D006801:Humans; D007710:Klebsiella Infections / Q000382:microbiology; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000201:enzymology*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D001618:beta-Lactamases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D047090:beta-Lactams / Q000378:metabolism / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D047090:beta-Lactams; D002442:Ceftazidime; D001618:beta-Lactamases