Escherichia coli (abbreviated as E. coli) are a large and diverse group of bacteria.  These bacteria are found in the environment, foods, and intestines of people and animals. The E. coli bacteria that are normally found in the intestines of people and animals are harmless. Those bacteria are an important part of a healthy human intestinal tract and aid in the digestive process. Although most strains of E. coli are harmless, others can make you sick.

Some strains of E. coli can cause diarrhea, while others cause urinary tract infections, respiratory illness and pneumonia, as well as other types of illnesses. The strains of E. coli that can cause diarrhea can be transmitted through contaminated water or food, or through contact with animals or persons.