Escherichia coli (E. coli) is a type of bacteria. Several strains of E. coli live in the large intestine and are typically harmless or beneficial. Some strains not normally found in the human gut, most notably O157:H7, produce Shiga toxin and are responsible for the potentially lethal food poisoning also called 'E. coli'. E. coli are well suited for genetic engineering and are the most studied and used bacteria in the field.