Background: Pathogenic bacteria are notorious for their high frequency of exchanging genetic material with other microbes living in the same environment.A few such mobile genetic elements (mobilome) include pathogenicity islands and antibiotic resistance islands.Methods: The mobilomes of three gram-negative bacterium Enterohemorrhagic Escherichia coli (EHEC) O157∶H7 were detected by in silico comparative genomic techniques.Results: We constructed a comprehensive map of Insertion Sequence (IS) elements in three completely sequenced strains of EHEC O157∶H7, i.e.Sakai, EDL933 and EC4115.13 IS elements are found to have full copies in EHEC O157∶H7 and five of them show transpositions after the divergence of the species E.coli.At least 20 genes, including transcriptional regulators and transporters, were disrupted by the insertions of IS elements in each of the three strains.Conclusions: EHEC O157∶H7 underwent frequent genomic recombinations with multiple mobile genetic element families, and its termination of replication (Ter) region represents a hot region for all these recombinations .