Shigella flexneri 2a str. 301

Shigella is a Gram-negative, non-sporulating, facultative anaerobe bacterium that causes dysentery or shigellosis in man. Shigella are highly invasive in the colon and the rectum, and are able to proliferate in the host cell cytoplasm, triggering an inflammatory reaction. Shigella was recognized as the etiologic agent for bacillary dysentery in the 1890's, and adopted as a genus in the 1950's and subgrouped into four species. However, a recent genetic study argues that Shigella emerged from multiple independent origins of E.coli 35'000-270'000 years ago and may not constitute a genus. Comparison of 20 E.coli/Shigella strains shows the core genome to be about 2000 genes while the pan-genome has over 18,000 genes. There are multiple, striking integration hotspots that are conserved across the genomes, corresponding to regions of abundant and parallel insertions and deletions of genetic material. (EBI Integr8)