Identification and Characterization of stx2 Converting Bacteriophage from Shiga-Toxin-Producing Escherichia coli O157 Strains of Animal Origin

In order to understand the characteristics of Stx2-converting bacteriophage and its role in stx virulence factor transmission between different E. coli strains, Stx2 bacteriophages were isolated from Shiga toxin-producing E. coli 0157 isolates of animal origin and phage characteristics were investigated. Three different virion morphologies of the purified phages were observed. All the Stx2 phages with double-stranded DNA had genome sizes in the range of 48 to 65 kb. The RFLP of these phages showed different patterns, although the SDS-PAGE protein profiles of these phages were similar. A stable lysogen with the stx2 was obtained after transfecting laboratory E. coli MC1061 with phage PhiHY. The lysogen was able to produce biologically active Stx2 toxin by Vera cell assay. Taken together, E. coli 0157 isolated from animal origin could produce infectious Stx2 phage. The plaque characterization and infectivity of the phage depended upon different E. coli hosts. Transduction of Stx2 phage and the increase in Stx toxin production after transduction are indicators of the potential risk of the stx2 phages in the emergence of new pathogens.