title: Carriage of stx2a differentiates clinical and bovine-biased strains of Escherichia coli O157.
abstract: BACKGROUND
  Shiga toxin (Stx) are cardinal virulence factors of enterohemorrhagic E. coli O157:H7 (EHEC O157). The gene content and genomic insertion sites of Stx-associated bacteriophages differentiate clinical genotypes of EHEC O157 (CG, typical of clinical isolates) from bovine-biased genotypes (BBG, rarely identified among clinical isolates). This project was designed to identify bacteriophage-mediated differences that may affect the virulence of CG and BBG.
  
  
  METHODS
  Stx-associated bacteriophage differences were identified by whole genome optical scans and characterized among >400 EHEC O157 clinical and cattle isolates by PCR.
  
  
  RESULTS
  Optical restriction maps of BBG strains consistently differed from those of CG strains only in the chromosomal insertion sites of Stx2-associated bacteriophages. Multiplex PCRs (stx1, stx2a, and stx2c as well as Stx-associated bacteriophage-chromosomal insertion site junctions) revealed four CG and three BBG that accounted for >90% of isolates. All BBG contained stx2c and Stx2c-associated bacteriophage-sbcB junctions. All CG contained stx2a and Stx2a-associated bacteriophage junctions in wrbA or argW.
  
  
  CONCLUSIONS
  Presence or absence of stx2a (or another product encoded by the Stx2a-associated bacteriophage) is a parsimonious explanation for differential virulence of BBG and CG, as reflected in the distributions of these genotypes in humans and in the cattle reservoir.
authors.affiliation: Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, United States of America.
authors.forename: Smriti
authors.initials: S
authors.lastname: Shringi
authors.forename: Carrie
authors.initials: C
authors.lastname: Schmidt
authors.forename: Kaya
authors.initials: K
authors.lastname: Katherine
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Brayton
authors.forename: Dale D
authors.initials: DD
authors.lastname: Hancock
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Besser
mesh_terms: D000818:Animals; D001435:Bacteriophages / Q000235:genetics / Q000378:metabolism; D002417:Cattle; D004927:Escherichia coli Infections / Q000235:genetics*; D019453:Escherichia coli O157 / Q000235:genetics / Q000472:pathogenicity; D006801:Humans; D022621:Shiga Toxin / Q000235:genetics / Q000378:metabolism; D022641:Shiga Toxin 2 / Q000235:genetics / Q000378:metabolism; D014774:Virulence / Q000235:genetics
chemical_list: D022641:Shiga Toxin 2; D022621:Shiga Toxin