Color enhanced scanning electron micrograph of Escherichia coli (E. coli). E. coli are present in the intestinal contents of animals and are thus also called the intestinal rods. They are used as indicators of contamination with fecal material. In the past, some of these originally harmless bacteria developed toxins and became a serious health hazard to humans and animals. Magnification 3000x @ 5x7(inches).