Plasmids and genes contributing to high-level quinolone resistance in Escherichia coli

Int J Antimicrob Agents. 2020 Jul;56(1):105987. doi: 10.1016/j.ijantimicag.2020.105987. Epub 2020 Apr 21.


Introduction: The importance of plasmid-mediated quinolone resistance (PMQR) in Enterobacterales and its high incidence has been emphasised many times. However, a clinical strain carrying more than two PMQR genes is rare. This study sequenced plasmid transconjugants from a donor strain carrying four different PMQR genes to establish their genetic locations.

Methods: An Escherichia coli clinical strain displayed remarkable quinolone resistance with a ciprofloxacin MIC of 1024 mg/L carrying four PMQR genes: qnrA1, qepA1, aac(6')1b-cr and oqxAB. When outcrossed to Escherichia coli J53 AziR, different PMQR genes were transferred and the resulting strains 7C and 8C were chosen for further characterisation. Plasmids were extracted and sequenced by the Illumina and Oxford Nanopore Technologies platforms. S1 nuclease-PFGE was used to estimate the number and size of plasmids.

Results: The parental strain had three plasmid bands, as determined by PFGE. Transconjugant 8C obtained three plasmids: pMG336 (162 647 bp, F18:A-:B1:C4) carrying oqxAB; pMG335 carrying qepA1 (73 874 bp, F2:A-:B-); and pMG334 (59 724 bp, IncN (ST5)) with qnrA1 and aac(6')1b-cr. Interestingly, strain 7C obtained plasmid pMG333 (134 435 bp), which was not present in the parental strain but was an IncN-IncF cointegrate of plasmids pMG334 and pMG335 linked via insertion sequence IS26.

Conclusion: This study described the complete nucleotide sequence of three plasmids carrying four PMQR genes in a single strain and the plasmid profile obtained after outcrosses. In addition, it described a cointegrate of two plasmids formed with flanking insertion sequences.

Keywords: Ciprofloxacin; Escherichia coli; IS26; Plasmid-mediated quinolone resistance (PMQR) genes; Plasmids.

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Base Sequence
  • Ciprofloxacin / pharmacology*
  • Drug Resistance, Bacterial / genetics*
  • Escherichia coli / drug effects*
  • Escherichia coli / genetics*
  • Escherichia coli / isolation & purification
  • Escherichia coli Infections / drug therapy
  • High-Throughput Nucleotide Sequencing
  • Humans
  • Microbial Sensitivity Tests
  • Plasmids / genetics
  • Sequence Analysis, DNA


  • Anti-Bacterial Agents
  • Ciprofloxacin