The food-borne pathogen, Escherichia coli O157:H7, has been associated with gastrointestinal disease and the life-threatening sequela hemolytic uremic syndrome. The genes for the virulence factor, Shiga toxin 2 (Stx2), in E. coli O157:H7 are encoded on a temperate bacteriophage under the regulation of the late gene promoter. Induction of the phage lytic cycle is required for toxin synthesis and release. We investigated the hypothesis that nonpathogenic E. coli could amplify Stx2 production if infected with the toxin-encoding phage. Toxin-encoding phage were incubated with E. coli that were either susceptible or resistant to the phage. The addition of phage to phage-susceptible bacteria resulted in up to 40-fold more toxin than a pure culture of lysogens, whereas the addition of phage to phage-resistant bacteria resulted in significantly reduced levels of toxin. Intestinal E. coli isolates incubated with Shiga toxin-encoding phage produced variable amounts of toxin. Of 37 isolates, 3 produced significantly more toxin than was present in the inoculum, and 1 fecal isolate appeared to inactivate the toxin. Toxin production in the intestine was assessed in a murine model. Fecal toxin recovery was significantly reduced when phage-resistant E. coli was present. These results suggest that the susceptibility of the intestinal flora to the Shiga toxin phage could exert either a protective or an antagonistic influence on the severity of disease by pathogens with phage-encoded Shiga toxin. Toxin production by intestinal flora may represent a novel strategy of pathogenesis.

Shiga toxin 2 (Stx2) from the foodborne pathogen Escherichia coli O157:H7 is encoded on a temperate bacteriophage. Toxin-encoding phages from C600::933W and from six clinical E. coli O157:H7 isolates were characterized for PCR polymorphisms, phage morphology, toxin production, and lytic and lysogenic infection profiles on O157 and non-O157 serotype E. coli. The phages were found to be highly variable, and even phages isolated from strains with identical pulsed-field gel electrophoresis profiles differed. Examination of crossplaquing and lysogeny profiles further substantiated that each phage is distinct; reciprocal patterns of susceptibility and resistance were not observed and it was not possible to define immunity groups. The interaction between Shiga toxin-encoding phage and intestinal E. coli was examined. Lytic infection was assessed by examining Shiga toxin production following overnight incubation with phage. While not common, lytic infection was observed, with a more-than-1,000-fold increase in Stx2 seen in one case, demonstrating that commensal E. coli cells can amplify Shiga toxin if they are susceptible to infection by the Shiga toxin-encoding phages. Antibiotic-resistant derivatives of the Stx2-encoding phages were used to examine lysogeny. Different phages were found to lysogenize different strains of intestinal E. coli. Lysogeny was found to occur more commonly than lytic infection. The presence of a diverse population of Shiga toxin-encoding phages may increase the pathogenic fitness of E. coli O157:H7.

The presence of commensal flora reduced colonization of Escherichia coli O157:H7 and production of Shiga toxin (Stx) in the murine intestine. Stx production was not detected in mice colonized with E. coli that were resistant to the Shiga toxin phage, but it was detected in mice colonized with phage-susceptible E. coli.

Choose your poison: Shiga toxins 1 and 2 are the major virulence factors of E. coli O157:H7. However, Shiga 2 is more potent than Shiga 1. Biotinylated glycoconjugates have been developed that differentiate between these structurally homologous toxins (see picture; R=OH: selective for Shiga 1; R=NHAc: selective for Shiga 2). These synthetic materials efficiently capture toxins without interference from the sample matrix.

Zucker gegen Gifte: Die Shiga‐Toxine 1 und 2 sind die wichtigsten Giftstoffe von E. coli O157:H7, wobei Shiga 2 wirksamer ist als Shiga 1. Biotinylierte Glycokonjugate können zwischen den strukturhomologen Toxinen unterscheiden (siehe Formel; R = OH: Shiga‐1‐selektiv; R = NHAc: Shiga‐2‐selektiv). Diese synthetischen Substanzen fangen die Toxine effizient und ohne Störung durch die Probenmatrix ein.