Newly identified bacteriophages carrying the stx2g Shiga toxin gene isolated from Escherichia coli strains in polluted waters

Shiga toxin-converting bacteriophages are the main vehicle involved in horizontal transmission of stx(1) and stx(2) genes, which has led to the current spread of stx genes among a high number of Escherichia coli serotypes and other enterobacteria. Several stx gene variants have been described, although some of the variants have never been isolated from inducible bacteriophages. In this study, two stx(2g)-carrying bacteriophages induced from two different E. coli O2:H25 strains isolated from different wastewater samples were characterized. These bacteriophages when transduced into Shigella sonnei retained their ability to produce Stx(2) protein. They had similar but not identical DNA restriction patterns, and similar host ranges. Electron microscopy studies showed that they had isometric capsids with short tails, which resembled phage 933W. However, DNA cross-hybridization studies showed that phage 933W was not closely related to stx(2g) bacteriophages. This first description of stx(2g)-carrying bacteriophages enlarges the list of stx-carrying bacteriophages involved in horizontal transmission of stx genes in the environment.