Characterization of a Shiga toxin-encoding temperate bacteriophage of Shigella sonnei

A Shiga toxin (Stx)-encoding temperate bacteriophage of Shigella sonnei str ain CB7888 was investigated for its morphology, DNA similarity, host range, and lysogenization in Shigella and Escherichia coli strains. Phage 7888 fo rmed plaques on a broad spectrum of Shigella strains belonging to different species and serotypes, including Stx-producing Shigella dysenteriae type 1 . With E. coli, only strains with rough lipopolysaccharide were sensitive t o this phage. The phage integrated into the genome of nontoxigenic S. sonne t. and laboratory E. coli K-12 strains, which became Stx positive upon lyso genization. Moreover, phage 7888 is capable of transducing chromosomal gene s in E. coli K-12. The relationships of phage 7888 with the E. coli Stx1-pr oducing phage H-19B and the E. colt. Stx2-producing phage 933W were investi gated by DNA cross-hybridization of phage genomes and by nucleotide sequenc ing of an 8,053-bp DNA region of the phage 7888 genome flanking the stx gen es. By these methods, a high similarity was found between phages 7888 and 9 33W. Much less similarity was found between phages H-19B and 7888. As in th e other Stx phages, a regulatory region involved in Q-dependent expression is found upstream of stxA and stxB (stx gene) in phage 7888. The morphology of phage 7888 was similar to that of phage 933W, which shows a hexagonal h ead and a short tail. Our findings demonstrate that six genes are naturally transferable and are expressed in strains of S. sonnet., which points to t he continuous evolution of human-pathogenic Shigella by horizontal gene tra nsfer.