coli are very small Gram-negative rods, as seen here at 1000
X magnification. Escherichia coli is a normal bacterial inhabitant of the large intestine of vertebrates, including
humans. It is beneficial to humans because it produces vitamins we
need and aids in digestion of food. However, some strains of E.
coli are pathogenic. For example, E.coli O157:H7
has been implicated in foodborne disease, causing bloody diarrhea.