Negatively stained Escherichia coli, K12 strain. The colon bacillus E. coli is a short, plump, gram negative, non-spore-forming, motile bacilli almost constantly present in the alimentary canal of humans. This rod-shaped bacterium moves using its hair-like flagellae. It is normally non-pathogenic in the intestinal tract. Outside the body, and under certain conditions, particularly in the urinary tract, E. coli is responsible for infections in other systems, and for enteritis in infants. Certain enteropathogenic strains are a principle cause of traveler's diarrhea. TEM, magnification: x12,500 at 70mm. x6250 at 35mm size.