Carriage of stx2a Differentiates Clinical and Bovine-Biased Strains of Escherichia coli O157

• Published in: PloS one Vol. 7; no. 12; p. e51572
• Main Authors: Shringi, Smriti, Schmidt, Carrie, Katherine, Kaya, Brayton, Kelly A., Hancock, Dale D., Besser, Thomas E.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 11.12.2012; Public Library of Science (PLoS)
• Subjects: Animals; Bacteriophages - genetics; Bacteriophages - metabolism; Beef cattle; Biology; Bovidae; Cattle; Chromosome rearrangements; Clinical isolates; Cytotoxicity; Disease; E coli; Epidemics; Escherichia coli; Escherichia coli Infections - genetics; Escherichia coli O157 - genetics; Escherichia coli O157 - pathogenicity; Gene mapping; Genes; Genetic aspects; Genomes; Genomics; Genotypes; Humans; Insertion; Mortality; Multiplexing; Pathology; Phages; Shiga toxin; Shiga Toxin - genetics; Shiga Toxin - metabolism; Shiga Toxin 2 - genetics; Shiga Toxin 2 - metabolism; Strains (organisms); Toxins; Veterinary Science; Virulence; Virulence - genetics; Virulence factors; United States > US
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0051572

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. Stx-associated bacteriophage differences were identified by whole genome optical scans and characterized among >400 EHEC O157 clinical and cattle isolates by PCR. 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. 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.