FIG. 2.

Mapping pch AGR-associated genome alterations in E. coli O157:H7 strains. (A) PCR products resulting from the anchored PCR on selected strains using the stxB and pch ProbeR primers. A 1-kb ladder is shown to the left, and the positions of the bands expected for pchA, pchB, pchC, and the unique pchX are indicated at right. (B) Maps illustrate the DNA sequences of the different pch-holin S cassettes. The lengths of the PCR products are indicated above the relevant map. (C) Distribution of pch-holin cassettes detected in strains representing the stepwise descent of the E. coli O157:H7 lineage. The ancestor numbering and strain information is from Wick et al. (77), and a colored square indicates presence of the pch-holin S PCR product of expected size from the pchB-holin S, pchA-holin S, pchC-holin S, and pchX-holin S regions. (D) Autoradiographs of PFGE Southern blots from strains digested with PmeI and probed with ³²P-labeled amplicons from internal segments of pchC. The strain names are indicated above the relevant lane, with lanes labeled M containing lambda concatemers. The three images in the panel were derived from different PFGE gels and are not necessarily aligned. (E) Circular map of the E. coli O157:H7 Sakai genome. The positions of PmeI restriction sites are shown around the circumference. On the innermost ring, the relative positions of the origin and terminus of replication are indicated along with the lengths of the two replichores. Moving outward, the next ring shows the relative positions of the different prophage (Sp1 to Sp18). The pchA (Sp4), pchB (Sp11), and pchC (Sp14) prophage are shown in dark blue, the stx₂ (Sp5) and stx₁ (Sp15) prophage are shown in light blue, and the remainder are shown in red. The next ring shows the relative positions of pchC-hybridizing segments (green).