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JAC Advance Access published online on June 17, 2006
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkl252
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© The Author 2006. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
Received April 25, 2006
Revised May 19, 2006
Accepted May 24, 2006

Original article

A novel ceftazidime-hydrolysing extended-spectrum {beta}-lactamase, CTX-M-54, with a single amino acid substitution at position 167 in the omega loop

Il Kwon Bae 1, Byung Ho Lee 1, Hyun Yong Hwang 1, Seok Hoon Jeong 1 *, Seong Geun Hong 2, Chulhun L. Chang 3, Hyo-Sun Kwak 4, Hyoung Jin Kim 5, and Hasik Youn 5

1 Department of Laboratory Medicine, Kosin University College of Medicine, 602-030, 34 Amnam-Dong, Suh-Gu, Busan, Korea
2 Department of Laboratory Medicine, Pochon CHA University College of Medicine, 463-712, 351 Yatap-Dong, Bundang-Gu, Sungnam, Korea
3 Department of Laboratory Medicine, Pusan National University School of Medicine, 602-739, Suh-Gu, Ami-Dong 1-10, Busan, Korea
4 Center for Food Safety Evaluation, Korea Food and Drug Administration, 122-704, 231 Jinheung-Ro, Eunpyung-Gu, Seoul, Korea
5 R&D Park, LG Life Sciences, Ltd, 305-380, 104-1 Moonji-Dong, Yuseong-Gu, Daejeon, Korea

* To whom correspondence should be addressed.
Seok Hoon Jeong, E-mail: kscpjsh{at}ns.kosinmed.or.kr


  Abstract

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 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 ~21 kbp that carries both blaSHV-2a and bla CTX-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.

Keywords: cefotaximase; ISEcp1; IS903.
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