Phylogenetic tree of IS 629 in E. coli O157:H7 and O55:H7 showing the three different IS 629 sub-types present on those five genomes. IS629 sub-type I differed from sub-type II by 4% (> 55 bp) and sub-type II differed from sub-type III by 5% (> 60 bp). IS629 sub-type II was only present in O55:H7 genome (A1/A2 CC) while sub-type I and III were present in all O157:H7 genomes (A6 CC). The evolutionary history was inferred using the Minimum Evolution method . The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. Bootstrap support when above 50% is shown at nodes. Sp- prophages; SpLE - prophage-like elements; and back - backbone.