Escherichia coli is a species of gram-negative chemoheterotrophic bacterium in the family Enterobacteriaceae. It is most commonly found in the lower intestinal tracts of endothermic animals such as mammals and dinosaurs. Many strains of E. coli exist; some are pathogenic and are the primary causative agent of food poisoning, while others are symbiotic and beneficial to their hosts, such as the strain which produces vitamin K2. The majority are generally harmless to their hosts. This is one of the best-studied species of bacteria in science due to its ubiquitous nature and the fact that it is very easy to cultivate in captivity.
