Computer artwork of the structure of an Escherichia coli bacterium. Shown are the pili and capsule. E. coli bacteria are a normal part of the intestinal flora in humans and other animals, where they aid digestion. However, some strains, for instance enterohaemorrhagic E. coli (EHEC), can produce a toxin (Shiga toxin) that leads to severe illness or even death. Normal strains can also produce infections in weakened or immunosuppressed people.