title: Detection of virulent Escherichia coli O157 strains using multiplex PCR and single base sequencing for SNP characterization.
abstract: OBJECTIVE
  To compare 167 Norwegian human and nonhuman Escherichia coli O157:H7/NM (nonmotile) isolates with respect to an A/T single nucleotide polymorphism (SNP) in the tir gene and to detect specific SNPs that differentiate STEC O157 into distinct virulence clades (1-3 and 8).
  
  
  RESULTS
  We developed a multiplex PCR followed by single base sequencing for detection of the SNPs, and examined the association among SNP genotype, virulence profile (stx and eae status), multilocus variable number of tandem repeats analysis (MLVA) profile and clinical outcome. We found an over-representation of the T allele among human strains compared to nonhuman strains, including 5/6 haemolytic-uraemic syndrome cases. Fourteen strains belonged to clade 8, followed by two clade 2 strains. No clade 1 nor 3 isolates were observed. stx1 in combination with either stx2(EDL933) or stx2c were frequently observed among human strains, whereas stx2c was dominating in nonhuman strains. MLVA indicated that only single cases or small outbreaks with E. coli O157 have been observed in Norway through the years 1993-2008.
  
  
  CONCLUSIONS
  We observed that the tir-255 A/T SNP and the stx status were different between human and nonhuman O157 strains. No major outbreaks were observed, and only a few strains were differentiated into the virulence clades 2 and 8.
  
  
  CONCLUSIONS
  The detection of virulence clade-specific SNPs enables the rapid designation of virulent E. coli O157 strains, especially in outbreak situations.
authors: Department of Foodborne Infections, The Norwegian Institute of Public Health, Oslo, Norway.
authors: K
authors: K
authors: Haugum
authors: L T
authors: LT
authors: Brandal
authors: I
authors: I
authors: Løbersli
authors: G
authors: G
authors: Kapperud
authors: B-A
authors: BA
authors: Lindstedt
mesh_terms: D004269:DNA, Bacterial / Q000235:genetics; D019453:Escherichia coli O157 / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000472:pathogenicity; D029968:Escherichia coli Proteins / Q000235:genetics; D005838:Genotype; D006801:Humans; D018598:Minisatellite Repeats; D058885:Multilocus Sequence Typing; D009664:Norway; D016133:Polymerase Chain Reaction / Q000379:methods*; D020641:Polymorphism, Single Nucleotide; D011956:Receptors, Cell Surface / Q000235:genetics; D022603:Shiga Toxins / Q000235:genetics; D014774:Virulence
chemical_list: D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D011956:Receptors, Cell Surface; D022603:Shiga Toxins; C109287:Tir protein, E coli