Characterization of a Shiga Toxin-Encoding Temperate Bacteriophage of Shigella sonnei

摘要

A Shiga toxin (Stx)-encoding temperate bacteriophage ofShigella sonnei strain CB7888 was investigated for its morphology, DNA similarity, host range, and lysogenization inShigella and Escherichia coli strains. Phage 7888 formed plaques on a broad spectrum of Shigella strains belonging to different species and serotypes, including Stx-producingShigella dysenteriae type 1. With E. coli, only strains with rough lipopolysaccharide were sensitive to this phage. The phage integrated into the genome of nontoxigenic S. sonneiand 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 relationships of phage 7888 with the E. coli Stx1-producing phage H-19B and the E. coli Stx2-producing phage 933W were investigated by DNA cross-hybridization of phage genomes and by nucleotide sequencing of an 8,053-bp DNA region of the phage 7888 genome flanking the stx genes. By these methods, 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 that of phage 933W, which shows a hexagonal head and a short tail. Our findings demonstrate that stx genes are naturally transferable and are expressed in strains of S. sonnei, which points to the continuous evolution of human-pathogenic Shigella by horizontal gene transfer.