Bacteriophage 2851 Is a Prototype Phage for Dissemination of the Shiga Toxin Variant Gene 2c in <i>Escherichia coli</i> O157:H7

<jats:title>ABSTRACT</jats:title> <jats:p> The production of Shiga toxin (Stx) (verocytotoxin) is a major virulence factor of <jats:italic>Escherichia coli</jats:italic> O157:H7 strains (Shiga toxin-producing <jats:italic>E. coli</jats:italic> [STEC] O157). Two types of Shiga toxins, designated Stx1 and Stx2, are produced in STEC O157. Variants of the Stx2 type (Stx2, Stx2c) are associated with high virulences of these strains for humans. A bacteriophage designated 2851 from a human STEC O157 encoding the Stx2c variant was described previously. Nucleotide sequence analysis of the phage 2851 genome revealed 75 predicted coding sequences and indicated a mosaic structure typical for lambdoid phages. Analyses of free phages and K-12 phage 2851 lysogens revealed that upon excision from the bacterial chromosome, the loss of a phage-encoded IS <jats:italic>629</jats:italic> element leads to fusion of phage <jats:italic>antA</jats:italic> and <jats:italic>antB</jats:italic> genes, with the generation of a recombined <jats:italic>antAB</jats:italic> gene encoding a strong antirepressor. In wild-type <jats:italic>E. coli</jats:italic> O157 as well as in K-12 strains, phage 2851 was found to be integrated in the <jats:italic>sbcB</jats:italic> locus. Additionally, phage 2851 carries an open reading frame which encodes an OspB-like type III effector similar to that found in <jats:italic>Shigella</jats:italic> spp. Investigation of 39 <jats:italic>stx</jats:italic> <jats:sub>2c</jats:sub> <jats:italic>E. coli</jats:italic> O157 strains revealed that all except 1 were positive for most phage 2851-specific genes and possessed a prophage with the same border sequences integrated into the <jats:italic>sbcB</jats:italic> locus. Phage 2851-specific sequences were absent from most <jats:italic>stx</jats:italic> <jats:sub>2c</jats:sub> -negative <jats:italic>E. coli</jats:italic> O157 strains, and we suggest that phage 2851-like phages contributed significantly to the dissemination of the Stx2c variant toxin within this group of <jats:italic>E. coli</jats:italic> . </jats:p>