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J Antimicrob Chemother. 2015 Jul;70(7):1969-72. doi: 10.1093/jac/dkv066. Epub 2015 Mar 18.

Third-generation cephalosporin resistance conferred by a chromosomally encoded blaCMY-23 gene in the Escherichia coli ST131 reference strain EC958.

Author information

1
Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia.
2
Plymouth University Peninsula Schools of Medicine and Dentistry, Plymouth PL4 8AA, UK.
3
Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia m.schembri@uq.edu.au.

Abstract

OBJECTIVES:

Escherichia coli ST131 is a globally disseminated MDR clone originally identified due to its association with the blaCTX-M-15 gene encoding an ESBL. It is thus assumed that blaCTX-M-15 is the major determinant for resistance to β-lactam antibiotics in this clone. The complete sequence of EC958, a reference strain for E. coli ST131, revealed that it contains a chromosomally located blaCMY-23 gene with an upstream ISEcp1 element as well as several additional plasmid-encoded β-lactamase genes. Here, we examined the genetic context of the blaCMY-23 element in EC958 and other E. coli ST131 strains and investigated the contribution of blaCMY-23 to EC958 resistance to a range of β-lactam antibiotics.

METHODS:

The genetic context of blaCMY-23 and its associated mobile elements was determined by PCR and sequencing. Antibiotic susceptibility testing was performed using Etests. The activity of the blaCMY-23 promoter was assessed using lacZ reporter assays. Mutations were generated using λ-Red-recombination.

RESULTS:

The genetic structure of the ISEcp1-IS5-blaCMY-23 mobile element was determined and localized within the betU gene on the chromosome of EC958 and five other E. coli ST131 strains. The transcription of blaCMY-23, driven by a previously defined promoter within ISEcp1, was significantly higher than other β-lactamase genes and could be induced by cefotaxime. Deletion of the blaCMY-23 gene resulted in enhanced susceptibility to cefoxitin, cefotaxime and ceftazidime.

CONCLUSIONS:

This is the first known report to demonstrate the chromosomal location of blaCMY-23 in E. coli ST131. In EC958, CMY-23 plays a major role in resistance to third-generation cephalosporins and cephamycins.

KEYWORDS:

AmpC β-lactamases; E. coli ST131; antibiotic resistance

PMID:
25786480
DOI:
10.1093/jac/dkv066
[Indexed for MEDLINE]

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