Comparative analysis of the Shiga toxin converting bacteriophage first detected in Shigella sonnei

Here we report the first complete nucleotide sequence of a Shiga toxin (Stx) converting phage from a Shigella sonnei clinical isolate that harbors stx1 operon, first identified in the chromosome of Shigella dysenteriae type 1. The phage named Shigella phage 75/02 Stx displayed Podoviridae morphology. It proved to be transferable to Escherichia coli K-12 strains, and cytotoxicity of the lysogenized strains was demonstrated in Vero cell cultures. Genomic analysis revealed that the prophage genome is circular and its size is 60,875 nt that corresponds to 76 ORFs. The genome of Shigella phage 75/02 Stx shows a great degree of mosaic structure and its architecture is related to lambdoid phages. All the deduced proteins, including the 37 hypothetical proteins showed significant homologies to Stx phage proteins present in databases. The phage uniformly inserted into the ynfG oxidoreductase gene framed by phage integrase and antirepressor genes in parental S. sonnei and in the three lysogenized K-12 strains C600, DH5α and MG1655. The Stx1 prophage proved to be stable in its bacterial hosts and remained inducible.