title: Spread of oqxAB in Salmonella enterica serotype Typhimurium predominantly by IncHI2 plasmids.
abstract: OBJECTIVE
  To investigate the prevalence and genetic environment of the multiresistance gene oqxAB in Salmonella enterica serotype Typhimurium isolated from food-producing animals.
  
  
  METHODS
  In this study, 63 Salmonella enterica serotype Typhimurium isolates were analysed for the presence of plasmid-mediated quinolone resistance determinants and mutations in the quinolone resistance-determining region by molecular methods (PCR/sequencing). The oqxAB-positive isolates were typed by pulsed-field gel electrophoresis (PFGE). Plasmids carrying oqxAB were studied by conjugation/transformation, replicon typing, Southern hybridization, long-range PCR and restriction fragment length polymorphism (RFLP).
  
  
  RESULTS
  The oqxAB, aac(6')-Ib-cr and qnrS1 genes were present alone or in combination in 20 (31.7%), 23 (36.5%) and 1 (1.6%) isolate, respectively. The oqxAB-positive isolates were clonally related, as determined by PFGE. All of the oqxAB-aac(6')-Ib-cr-positive isolates carried transferable IncHI2-type plasmids containing an oqxAB cassette and an incomplete class 1 integron harbouring aac(6')-Ib-cr, blaOXA-1, catB3, arr3, qacEΔ1 and sul1. Meanwhile, 6 of 15 plasmids carrying both oqxAB and aac(6')-Ib-cr showed identical RFLP patterns.
  
  
  CONCLUSIONS
  The results suggest that both clonal expansion and horizontal transmission of IncHI2-type plasmids containing oqxAB and aac(6')-Ib-cr may be involved in the spread of oqxAB in Salmonella Typhimurium isolates in food-producing animals in China. There is a great need to monitor the potential dissemination of this multiresistance gene.
authors.affiliation: Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, P. R. China.
authors.forename: Liang
authors.initials: L
authors.lastname: Li
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Liao
authors.forename: Yurong
authors.initials: Y
authors.lastname: Yang
authors.forename: Jian
authors.initials: J
authors.lastname: Sun
authors.forename: Lulu
authors.initials: L
authors.lastname: Li
authors.forename: Baotao
authors.initials: B
authors.lastname: Liu
authors.forename: Shoushen
authors.initials: S
authors.lastname: Yang
authors.forename: Jun
authors.initials: J
authors.lastname: Ma
authors.forename: Xue
authors.initials: X
authors.lastname: Li
authors.forename: Qijing
authors.initials: Q
authors.lastname: Zhang
authors.forename: Yahong
authors.initials: Y
authors.lastname: Liu
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics*; D015139:Blotting, Southern; D002681:China; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D022761:Gene Transfer, Horizontal; D005838:Genotype; D006801:Humans; D058889:Molecular Typing; D010957:Plasmids / Q000145:classification*; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D015363:Quinolones / Q000494:pharmacology; D012486:Salmonella typhimurium / Q000145:classification / Q000235:genetics*; D017422:Sequence Analysis, DNA
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D015363:Quinolones
keywords: Enterobacteriaceae; PFGE; aac(6′)-Ib-cr; plasmid-mediated quinolone resistance; plasmids