Escherichia coli (E. coli) is classified as a rod-shaped, Gram-negative bacterium in the family Enterobacteriaceae. Most E. coli strains do not cause disease, but virulent strains can cause gastroenteritis, urinary tract infections, neonatal meningitis, hemorrhagic colitis, and Crohn's disease. The bacterium mainly inhabits the lower intestinal tract of warm-blooded animals, including humans, and is often discharged into the environment through faeces or wastewater effluent. Fecal oral transmission is the major route through which pathogenic strains of the bacterium cause disease. Cells are able to survive outside the body for a limited amount of time, which makes them potential indicator organisms to test environmental samples for fecal contamination. Also, E. coli is the most widely studied prokaryotic model organism, and an important species in the fields of biotechnology and microbiology.