title: Genotypic characterization to identify markers associated with putative hypervirulence in Swedish Escherichia coli O157:H7 cattle strains.
abstract: OBJECTIVE
  To establish whether investigated subtyping methods could identify any specific characteristics that distinguish Swedish VTEC O157:H7 strains isolated from cattle farms associated with human enterohaemorrhagic Escherichia coli (EHEC) cases from cattle strains isolated in prevalence studies.
  
  
  RESULTS
  Strains (n = 32) isolated in a dairy herd prevalence study and strains isolated from farms associated with human cases (n = 13) were subjected to typing. Partial sequencing of the vtx(2) genes could not identify any unique variants of vtx(2) or vtx(2c) in strains associated with human cases. A specific variant of VTEC O157:H7, which was overrepresented among farms associated with human cases (P = 0·01), was by two different single-nucleotide-polymorphism (SNP) assays identified as clade 8, a subgroup of VTEC O157:H7 strains considered to be putatively hypervirulent. Multi-locus variable number tandem repeat analysis (MLVA) typing of all strains produced similar results as pulsed-field gel electrophoresis (PFGE) typing regarding clustering of the strains, but MLVA distinguished slightly better among strains than PFGE.
  
  
  CONCLUSIONS
  In Sweden, VTEC O157:H7 strains from the putatively hypervirulent clade 8 are overrepresented among isolates from cattle farms associated with human cases compared with VTEC O157:H7 strains isolated in prevalence studies.
  
  
  CONCLUSIONS
  Real-time PCR SNP typing for clade 8 can be used to identify cattle farms that are at higher risk of causing EHEC infections in humans.
authors.affiliation: Department of Bacteriology, National Veterinary Institute, Uppsala, Sweden. erik.eriksson@sva.se
authors.forename: E
authors.initials: E
authors.lastname: Eriksson
authors.forename: R
authors.initials: R
authors.lastname: Söderlund
authors.forename: S
authors.initials: S
authors.lastname: Boqvist
authors.forename: A
authors.initials: A
authors.lastname: Aspan
mesh_terms: D000818:Animals; D002417:Cattle / Q000382:microbiology*; D016521:Electrophoresis, Gel, Pulsed-Field; D004927:Escherichia coli Infections / Q000382:microbiology; D019453:Escherichia coli O157 / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification / Q000472:pathogenicity*; D005819:Genetic Markers; D005838:Genotype; D006801:Humans; D058889:Molecular Typing / Q000379:methods*; D058885:Multilocus Sequence Typing; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide; D013548:Sweden; D014774:Virulence / Q000235:genetics
chemical_list: D005819:Genetic Markers