Circular diagram comparing the chromosomes of E. coli strains. The red circles show genes shared between different E.coli strains, with the outermost red circle being E. coli 55989. The magenta circle shows the 2001 outbreak strain, whilst the blue and green circles show genes shared with a Salmonella and a Shigella, respectively. Matches to the Shiga toxin encoding virus are shown in black under the green circle. This virus was present in the 2001 outbreak strain, and in E. coli O157:H7, but not in 55989.