Phylogenetic analysis of sequenced E. coli strains. Phylogenetic relationships based on seven housekeeping genes (adk, fumC, gyrB, icd, mdh, purA, and recA). Strains cluster into phylogroups; W can be found in group B1, whereas the other three laboratory strains are in group A. Escherichia fergusonii (ATCC 35469) was used as an out-group. The tree shows bootstrap values (percentage per 1000 replicates). The scale bar represents divergence time.