Transmission electron micrograph of ultra-thin section of Escherichia coli. The colon bacillus E. coli is a short, plump, gram negative, non-spore-forming, motile bacilli almost constantly present in the alimentary canal of man. It is normally nonpathogenic in the intestinal tract. Outside the body and under certain conditions, particularly in the urinary tract, E. coli is responsible for infections in the other systems and for enteritis in infants. Certain enteropathogenic strains are a principal cause of traveler's diarrhea. Magnification: x16,500 at 70mm.