Figure 1. Correlation between evolutionary lineages and distribution of two types of rfbE genes among O157:H7/non-H7 stains.

21 fully sequenced E coli strains were used as references. The phylogenetic tree was constructed based on concatenated sequences of seven housekeeping genes. E. coli phylogroups (A, B1, B2, D and E) were determined by comparing with sequences from the ECOR collection. O157:H7/non-H7 strains carrying “Sakai-type rfbE” and “PV01-185-type rfbE” are indicated by clear and gray boxes, respectively. Six O157 strains indicated by asterisks were used for the sequence comparisons of O157-antigen gene clusters and their flanking regions.