Journal
JOURNAL OF ANTIMICROBIAL CHEMOTHERAPY
Volume 58, Issue 2, Pages 315-319Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jac/dkl252
Keywords
cefotaximase; ISEcp1; IS903
Ask authors/readers for more resources
Objectives: 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 bla(CTX-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 similar to 21 kbp that carries both bla(SHV-2a) and bla(CTX-M-54) beta-lactamase genes, along with two other plasmids. The bla(CTX-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
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available