Molecular and kinetic comparison of the novel extended-spectrum beta-lactamases CTX-M-25 adn CTX-M-26

Research output: Contribution to journalArticle


  • DA Boyd
  • N Brenwald
  • M MIller
  • JM Andrews
  • Richard Wise
  • MR Mulvey

Colleges, School and Institutes


CTX-M-25 is a novel extended-spectrum beta-lactamase isolated from a single Canadian Escherichia coli isolate. Susceptibility testing demonstrated that this enzyme confers resistance to both cefotaxime and ceftazidime, but the level of resistance was reduced with the addition of beta-lactamase inhibitors. The bla(CTX-M-25) gene was detected on a 111-kb plasmid. It is a member of the CTX-M-8 group and has the closest amino acid identity (99%; three amino acid substitutions) with CTX-M-26. The bla(CTX-M-26) gene was detected on a 100-kb plasmid isolated from a Klebsiella pneumoniae strain from the United Kingdom, and plasmid profiling revealed that it showed some homology to the bla(CTX-M-25)-harboring plasmid. Both CTX-M genes were located downstream of ISEcp1, although the copy upstream of bla(CTX-M-25) was disrupted by IS50-A. Comparative kinetic studies of recombinant CTX-M-25 and CTX-M-26 enzymes showed that CTX-M-25 has a higher level of ceftazidime hydrolysis (kcat values, 33 and 0.005 s(-1) for CTX-M-25 and CTX-M-26, respectively).


Original languageEnglish
Pages (from-to)4829-34
Number of pages6
JournalAntimicrobial Agents and Chemotherapy
Publication statusPublished - 1 Jan 2004