Bacteria are the most numerous group of organisms. Most of these one-cell organisams are necessary to sustain life other macro-organisms on Earth. These bacteria were important in biological evolution, and today are the basis of each of the food chain in nature. They are present in soil and water. Perform a desirable chemical processes and is applied in various economic activities. Than 1,500 described species of bacteria, only a hundred kinds of human pathogens. Escherichia coli, one of the main species of bacteria that live in the lower part of the digestive tract of mammals. Necessary for proper digestion of food, and participate in the intestinal flora. Its presence in groundwater is usually an indicator of fecal infection. Classified in the group of Enterobacteriaceae. There are different strains of E. coli that produce potentially lethal toxins, such as E. coli O157: H7. Food poisoning caused by E. coli may be the result of eating unwashed vegetables and undercooked meat. In the field of waste water management is Escherichia coli very early showed an excellent indicator of the level of water pollution. Because of its omnipresent the Escherichia coli often studied in microbiology, and increasingly in molecular biology. Its structure is completely known. Plays an important role in modern biological engineering. Researchers often use a bacteria as "factories" for the production of large amounts of DNA and / or protein. One of the first major application of recombinant DNA technology was just genetic manipulation of Escherichia coli to produce insulin in patients with diabetes.