Dissemination and characterization of plasmids carrying oqxAB-bla CTX-M genes in Escherichia coli isolates from food-producing animals

PLoS One. 2013 Sep 9;8(9):e73947. doi: 10.1371/journal.pone.0073947. eCollection 2013.


Background: The association of PMQR and ESBLs in negative-bacteria isolates has been of great concern. The present study was performed to investigate the prevalence of co-transferability of oqxAB and bla CTX-M genes among the 696 Escherichia coli (E. coli) isolates from food-producing animals in South China, and to characterize these plasmids.

Methods: The ESBL-encoding genes (bla(CTX-M), bla(TEM) and bla(SHV)), and PMQR (qnrA, qnrB, qnrS, qnrC, qnrD, aac(6')-Ib-cr, qepA, and oqxAB) of these 696 isolates were determined by PCR and sequenced directionally. Conjugation, S1 nuclease pulsed-field gel electrophoresis (PFGE) and Southern blotting experiments were performed to investigate the co-transferability and location of oqxAB and bla(CTX-M). The EcoRI digestion profiles of the plasmids with oqxAB-bla(CTX-M) were also analyzed. The clonal relatedness was investigated by PFGE.

Results: Of the 696 isolates, 429 harbored at least one PMQR gene, with oqxAB (328) being the most common type; 191 carried bla(CTX-M), with bla(CTX-M-14) the most common. We observed a significant higher prevalence of bla(CTX-M) among the oqxAB-positive isolates (38.7%) than that (17.4%) in the oqxAB-negative isolates. Co-transferability of oqxAB and bla(CTX-M) was found in 18 of the 127 isolates carrying oqxAB-bla(CTX-M). These two genes were located on the same plasmid in all the 18 isolates, with floR being on these plasmids in 13 isolates. The co-dissemination of these genes was mainly mediated by F33:A-: B- and HI2 plasmids with highly similar EcoRI digestion profiles. Diverse PFGE patterns indicated the high prevalence of oqxAB was not caused by clonal dissemination.

Conclusion: bla(CTX-M) was highly prevalent among the oqxAB-positive isolates. The co-dissemination of oqxAB-bla(CTX-M) genes in E. coli isolates from food-producing animals is mediated mainly by similar F33:A-: B- and HI2 plasmids. This is the first report of the co-existence of oqxAB, bla(CTX-M), and floR on the same plasmids in E. coli.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anti-Bacterial Agents / pharmacology
  • Chickens
  • Conjugation, Genetic
  • Drug Resistance, Bacterial / genetics
  • Ducks
  • Escherichia coli / classification*
  • Escherichia coli / drug effects
  • Escherichia coli / genetics*
  • Escherichia coli / isolation & purification
  • Geese
  • Microbial Sensitivity Tests
  • Molecular Typing
  • Plasmids / genetics*
  • Quinolones / pharmacology
  • Swine
  • beta-Lactamases / genetics*


  • Anti-Bacterial Agents
  • Quinolones
  • beta-Lactamases

Grant support

This work was supported by the National Science Fund for Distinguished Young Scholars (Grant No. 31125026), the Special Fund for Agro-scientific Research in the Public Interest (Grant No.201203040) and the National Natural Science Foundation of China (Grant No. U1201214). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.