Enterohemorrhagic Escherichia coli (EHEC) of serotype O157:H7 has been implicated in food-borne illnesses worldwide. An evolutionary model was proposed in which the highly pathogenic EHEC O157:H7 serotype arose from its ancestor, enteropathogenic E. coli (EPEC) O55:H7 (sorbitol fermenting {[}SOR+] and beta-glucuronidase positive {[}GUD(+)]), through sequential gain of virulence, phenotypic traits, and serotype change. Here we report six draft genomes of strains belonging to this evolutionary model:two EPEC O55:H7 (SOR+ GUD(+)) strains, two nonmotile EHEC O157:H- strains (SOR+ GUD(+)) containing plasmid pSFO157, one EHEC O157:H7(SOR- GUD(+)) strain, and one O157:H7 strain containing plasmid pSFO157 (SOR+ GUD(+)).