title: [Identification of harboring stx2::IS1203 Escherichia coli O157:H7 strains isolated in China].
abstract: OBJECTIVE
  To understand the variation of Shiga toxin (stx) genes of Escherichia coli O157:H7 strains isolated in China.
  
  
  METHODS
  Polymerase chain reaction (PCR) was used to identity the types of stx genes and the nucleotide sequences of the amplified stex variants genes were determined. Compare to the cytotoxicity of Stx,variants were tested by HeLa cell assay.
  
  
  RESULTS
  We found novel stx2 genes in 3 of 289 strains of Shiga toxin-producing E. coli O157:H7 isolated from 1999 to 2002 in China. The novel stx2 genes were inserted by a 1.3-kb insertion sequence (IS) and the nucleotide sequences of IS showed 100% homology with that of IS1203 variant (IS1203v). The IS1203v inserted in the stx2 genes of three E. coli O157:H7 strains at different sites and the direction of the open reading frames (ORFs) of IS1203v of each strain was different. In addition to the above mentioned findings, the nucleotide sequences of three stx2 genes were completely identical and the type of the three Stx2 was Stx2 prototype. Compare to the cytotoxicity of Stx2 prototype, the novel Stx2 was found to be obviously lower.
  
  
  CONCLUSIONS
  E. coli O157:H7 strains harboring stx2::IS1203v genes were isolated in China. Consequently, the results of HeLa cell assay showed that the insertion of IS1203v could lead to low cytotoxicity of Stx2.
authors.affiliation: State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing 102206, China.
authors.forename: Xia
authors.initials: X
authors.lastname: Luo
authors.forename: Chang-yun
authors.initials: CY
authors.lastname: Ye
authors.forename: Fang
authors.initials: F
authors.lastname: Li
authors.forename: Hua
authors.initials: H
authors.lastname: Wang
authors.forename: Jun
authors.initials: J
authors.lastname: Ren
authors.forename: Huai-qi
authors.initials: HQ
authors.lastname: Jing
authors.forename: Jian-guo
authors.initials: JG
authors.lastname: Xu
mesh_terms: D001483:Base Sequence; D002681:China; D004269:DNA, Bacterial / Q000235:genetics; D019453:Escherichia coli O157 / Q000235:genetics* / Q000302:isolation & purification; D005798:Genes, Bacterial; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D022641:Shiga Toxin 2 / Q000235:genetics*
chemical_list: D004269:DNA, Bacterial; D022641:Shiga Toxin 2