Effect of plasmids harbouring blaCTX-M on the virulence and fitness of Escherichia coli ST131 isolates

Int J Antimicrob Agents. 2015 Aug;46(2):214-8. doi: 10.1016/j.ijantimicag.2015.04.012. Epub 2015 Jun 4.


The effect of plasmids harbouring blaCTX-M on the virulence and fitness on Escherichia coli sequence type 131 (ST131) isolates was investigated. Plasmids harbouring blaCTX-M-14 or blaCTX-M-15 were transferred by transconjugation into five non-extended-spectrum β-lactamase (ESBL)-producing ST131 isolates. Clinical non-ESBL-producing ST131 isolates demonstrated a higher degree of biofilm formation and serum resistance compared with CTX-M-producing ST131 isolates. In addition, non-ESBL-producing isolates were more competitive than CTX-M-producing isolates. Transconjugants showed no significant defect in growth rate and competitiveness compared with their hosts. However, serum resistance and biofilm formation were diminished in the transconjugants. In conclusion, non-ESBL-producing E. coli ST131 isolates were more competitive and virulent than CTX-M-producing E. coli ST131 isolates. However, transconjugants harbouring blaCTX-M were no less competitive than their susceptible hosts, which may partially explain the global dissemination of CTX-M-14- and CTX-M-15-producing E. coli ST131 isolates, in addition to their increased antimicrobial resistance.

Keywords: CTX-M-14; CTX-M-15; Plasmid; ST131; Sequence type 131.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biofilms / growth & development
  • Blood Bactericidal Activity
  • Conjugation, Genetic
  • Escherichia coli / classification
  • Escherichia coli / enzymology*
  • Escherichia coli / genetics
  • Escherichia coli / physiology*
  • Escherichia coli Infections / microbiology
  • Humans
  • Plasmids*
  • Transformation, Bacterial
  • Virulence
  • beta-Lactamases / genetics
  • beta-Lactamases / metabolism*


  • beta-lactamase CTX-M-14
  • beta-lactamase CTX-M-15
  • beta-Lactamases