FIG 5.

Extended evolutionary scenario for SF EHEC O157 plasmids based on sequence analyses of the plasmids of SF EHEC O157:H⁻ strain 258/98. The pSFO157 plasmid of the A4 clonal complex (SF EHEC O157:H⁻ strains of the German clone and the Scottish clone), represented by pSFO157 3072/96, evolved from a common O157 ancestor plasmid of a hypothetical intermediate strain of the A3 clonal complex by acquisition of the sfpAHCDJFG operon. From pSFO157 of the A4 complex, pSFO157 258/98-1 (79 kb) (A8 clonal complex; Czech clone) evolved via deletion of a 41,534-bp region by homologous recombination, leading to loss of the hlyCABD and etpCDEFGHIJKLMNO operons but retention of the sfpAHCDJFG operon. In addition, the A8 clonal complex strains acquired an EHEC O157-unrelated plasmid, pSFO157 258/98-2 (86 kb), which is 98% similar to pSF-468-2 (92.7 kb) (GenBank accession no. CP012627) from an ExPEC strain. The clonal complexes A5, A6, and A7 represent the evolution of NSF EHEC O157:H7 plasmids and were previously described in detail (31). (Adapted from reference 31 with permission.)