title: Dissemination and characterization of plasmids carrying oqxAB-bla CTX-M genes in Escherichia coli isolates from food-producing animals.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: College of Veterinary Medicine, National Reference Laboratory of Veterinary Drug Residues (SCAU), South China Agricultural University, Guangzhou, Guangdong, China.
authors.forename: Bao-Tao
authors.initials: BT
authors.lastname: Liu
authors.forename: Qiu-E
authors.initials: QE
authors.lastname: Yang
authors.forename: Liang
authors.initials: L
authors.lastname: Li
authors.forename: Jian
authors.initials: J
authors.lastname: Sun
authors.forename: Xiao-Ping
authors.initials: XP
authors.lastname: Liao
authors.forename: Liang-Xing
authors.initials: LX
authors.lastname: Fang
authors.forename: Shou-Shen
authors.initials: SS
authors.lastname: Yang
authors.forename: Hui
authors.initials: H
authors.lastname: Deng
authors.forename: Ya-Hong
authors.initials: YH
authors.lastname: Liu
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002645:Chickens; D003227:Conjugation, Genetic; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004372:Ducks; D004926:Escherichia coli / Q000145:classification* / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D005777:Geese; D008826:Microbial Sensitivity Tests; D058889:Molecular Typing; D010957:Plasmids / Q000235:genetics*; D015363:Quinolones / Q000494:pharmacology; D013552:Swine; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D015363:Quinolones; D001618:beta-Lactamases
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