Genotypic diversification of various Escherichia coli and Shigella spp. based on highly conserved housekeeping genes mdh (A) and rpoB (B). EHEC, EIEC, EPEC, STEC and ATCC 25922 E. coli form E. coli group; S. dysenteriae, S. flexneri 2a, S. flexneri 5a, S. flexneri, S. boydii and S. sonnei from Shigella group were used to construct double-locus variant–based phylogeny. EHEC, enterohaemorrhagic E. coli; EIEC, enteroinvasive E. coli; EPEC, enteropathogenic E. coli; STEC, Shiga toxin–producing E. coli.