of enterohaemorrhagic Escherichia coli O157 pathogenesis using basic symbols. The right-hand illustration shows enterohaemorrhagic E. coli interactions with an epithelial cell.Escherichia coli O157 : H7 is a zoonotic diarrhoeal pathogen of worldwide importance. It belongs to a subset of Shiga toxin-producing E. coli that can form attaching and effacing lesions on intestinal epithelia via the action of a type 3 secretion system that injects bacterial effectors into enterocytes. Infections in humans often arise from contaminated food or direct environmental exposure and can involve life-threatening Shiga toxin-dependent sequelae. In the three decades since E. coli O157 : H7 was first recognized intensive research has helped to unravel the basis of pathogenesis, but few effective options for prevention and treatment of infections exist.