Strauch E, Lurz R, Beutin L (2001): Characterization of a Shiga Toxin-Encoding Temperate Bacteriophage of Shigella sonnei
Infect. Immun. 69 (12): 7588-7595.

A Shiga toxin (Stx) encoding temperate bacteriophage of Shigella sonnei strain CB7888 was investigated for its morphology, DNA similarity, host range and lysogenization in Shigella and Escherichia coli strains. Phage 7888 formed plaques on on a broad spectrum of Shigella strains belonging to different species and serotypes including Stx producing S. dysenteriae type 1. With E. coli, only strains with rough LPS were sensitive to this phage. The phage integrated into the genome of non-toxigenic S. sonnei and laboratory E. coli K-12 strains, which became Stx positive upon lysogenization. Moreover, phage 7888 is capable of transducing chromosomal genes in E. coli K-12. The relationship of phage 7888 with the E. coli Stx1 phage H-19B and Stx2 phage 933W was investigated by DNA crosshybridization of phage genomes and by nucleotide sequencing of an 8053 bp DNA region of the phage 7888 genome flanking the stx genes. By this, a high similarity was found between phages 7888 and 933W. Much less similarity was found between phages H-19B and 7888. As in the 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 phage 933W showing a hexagonal head and a short tail. Our findings demonstrate that stx genes are naturally transferable and expressed in strains of S. sonnei, which points to the continuous evolution of human pathogenic Shigella by horizontal gene transfer.