False-colour transmission electron micrograph of the bacterium Escherichia coli, a normal inhabitant of the human intestine, in the act of dividing. Under certain conditions E. coli bacteria may become harmful & cause infection in the intestinal or urinogenital tracts. This specimen is in the early stages of binary fission, the process by which the bacterium divides in two. E. coli is the organism most commonly used in genetic engineering experiments. Magnification: x22,175 at 6x4.5cm size.