Complete DNA sequence and analysis of the large virulence plasmid of Shigella flexneri

The complete sequence analysis of the 210-kb Shigella flexneri 5a virulence plasmid was determined. Shigella spp. cause dysentery and diarrhea by inva sion and spread through the colonic mucosa. Most of the known Shigella viru lence determinants are encoded on a large plasmid that is unique to virulen t strains of shigella and enteroinvasive Escherichia coli; these known gene s account for approximately 30 to 35% of the virulence plasmid. In the comp lete sequence of the virulence plasmid, 286 open reading frames (ORFs) were identified. An astonishing 153 (53%) of these were related to known and pu tative insertion sequence (IS) elements; no known bacterial plasmid has pre viously been described with such a high proportion of IS elements. Pour new IS elements were identified. Fifty putative proteins show no significant h omology to proteins of known function; of these, 18 have a G+C content of l ess than 40%, typical of known virulence genes on the plasmid. These 18 con stitute potentially unknown virulence genes, Two alleles of shet2 and five alleles of ipaH were also identified on the plasmid, Thus, the plasmid sequ ence suggests a remarkable history of IS mediated acquisition of DNA across bacterial species. The complete sequence sill permit targeted characteriza tion of potential new Shigella virulence determinants.