title: Third-generation cephalosporin resistance conferred by a chromosomally encoded blaCMY-23 gene in the Escherichia coli ST131 reference strain EC958.
abstract: OBJECTIVE
  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.
authors: Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia.
authors: Minh-Duy
authors: MD
authors: Phan
authors: Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia.
authors: Kate M
authors: KM
authors: Peters
authors: Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia.
authors: Sohinee
authors: S
authors: Sarkar
authors: Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia.
authors: Brian M
authors: BM
authors: Forde
authors: Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia.
authors: Alvin W
authors: AW
authors: Lo
authors: Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia.
authors: Mitchell
authors: M
authors: Stanton-Cook
authors: Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia.
authors: Leah W
authors: LW
authors: Roberts
authors: Plymouth University Peninsula Schools of Medicine and Dentistry, Plymouth PL4 8AA, UK.
authors: Mathew
authors: M
authors: Upton
authors: Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia.
authors: Scott A
authors: SA
authors: Beatson
authors: Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia m.schembri@uq.edu.au.
authors: Mark A
authors: MA
authors: Schembri
mesh_terms: D019677:Artificial Gene Fusion; D018550:Cephalosporin Resistance; D002876:Chromosomes, Bacterial; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D017930:Genes, Reporter; D020071:Interspersed Repetitive Sequences; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D017422:Sequence Analysis, DNA; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*
chemical_list: D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D001616:beta-Galactosidase; D001618:beta-Lactamases
keywords: AmpC β-lactamases; E. coli ST131; antibiotic resistance