Escherichia coli is the name given to bacteria that are part of the intestinal microflora of humans and animals, and also make up a significant part of the human microbiota, if we consider it as a whole, even without giving preference to a specific area - for example, the oral cavity. But at the same time, most pathogenic forms have obvious differences with the normal strain of E. coli and can differ significantly from the “useful” rod in terms of size, structural features and enzymatic properties, which determine the characteristics of the metabolism and biochemical response of microorganisms to external factors. Simply put, E. coli in humans or animals plays an extremely important role, acting as an additional element of the body's immune defense. But opportunistic species are involved in many serious diseases.