Complete sequence of the large virulence plasmid pSFO157 of the sorbitol-fermenting enterohemorrhagic Escherichia coli O157:H− strain 3072/96

The large virulence plasmid pSFO157 of sorbitol-fermenting E. coli O157:H− strain 3072/96 has a size of 121,239 bp and contains 96 open reading frames >50 bp. It is therefore 29,162 bp larger (ca. 32%) than plasmid pO157 of E. coli O157:H7 strain EDL933. Major differences between the plasmids are the absence of katP, espP, and toxB in pSFO157 and, instead of these, the presence of the sfp fimbriae gene cluster and a large part of an F-plasmid transfer region, the latter accounting for most of the additional DNA. The differences in the order of the genes and their composition, as well as the presence of a number of replication-associated genes and mobile genetic elements suggests that the large E. coli O157 virulence plasmids have a complex evolutionary origin.