E. coli

E. coli, (Escherichia coli), species of bacterium that normally inhabits the large intestine and lower intestinal tract of humans and other animals. Escherichia coli (E. coli) is a prokaryotic bacterium; most strains are harmless and form part of the community of microorganisms known as the gut microbiota. Some strains, however, have acquired mutations and or genes that encode disease-causing traits can lead to strains that cause diarrhea by giving off toxins, invading the intestinal lining, or sticking to the intestinal wall. Certain disease-causing strains are important sources of foodborne illness, while others can cause infections outside the digestive system.

E. coli is one of the most extensively studied organisms in biology. Its relatively simple structure, rapid reproduction, and ease of growth in the laboratory have made it an important model organism for investigating genetics, evolution, metabolism, and other fundamental biological processes. Scientists also use modified E. coli in biotechnology to manufacture useful substances, including human proteins.

Structure and reproduction

E. coli is rod-shaped and surrounded by a cell membrane and cell wall. Some strains possess flagella, threadlike structures that enable the cells to move. Being prokaryotic, E. coli cells lack a nucleus and the membrane-bound organelles found in the cells of plants, animals, and other eukaryotes. Most of its genetic information is contained in a single circular chromosome located within the cell cytoplasm. E. coli may also contain smaller rings of DNA known as plasmids, which can carry additional genes.

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E. coli reproduces asexually through binary fission, in which a cell copies its DNA and divides into two daughter cells. Under favorable conditions, populations can grow rapidly. Genetic variation arises through mutation and through the exchange or acquisition of DNA. This ability to gain new genes helps explain why strains belonging to the same bacterial species can have very different characteristics.

E. coli and disease

Pathogenic, or disease-causing, strains of E. coli possess biological features that harmless strains lack. Depending on the strain, these bacteria may produce toxins, attach tightly to intestinal cells, or invade tissues. Some pathogenic strains spread through the fecal-oral route, in which bacteria from fecal matter reach another person’s mouth, often through contaminated food or water. Infection can occur from such sources as undercooked contaminated meat, unpasteurized products, contaminated produce or water, or contact with infected animals or people.

An important group, known as Shiga toxin-producing E. coli (STEC), produces toxins that can damage the intestinal lining and small blood vessels. Infection may cause severe abdominal cramps and bloody diarrhea. A well-known STEC strain is E. coli O157. In some patients, particularly young children, STEC infection can lead to hemolytic uremic syndrome (HUS), a serious condition involving destruction of red blood cells, a reduction in blood platelets, and acute kidney injury. Antibiotics generally are not recommended for suspected STEC infection because some evidence indicates that they may increase the risk of HUS. Maintaining fluid balance is an important part of treatment.

Not all E. coli infections involve the digestive tract. Strains originating in the intestine are also a major cause of urinary tract infections (UTIs) when they enter the urinary system. Other infections caused by E. coli include bacteremia, in which bacteria enter the bloodstream, and sepsis, a potentially life-threatening response to infection, as well as some cases of meningitis in newborns.

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Prevention of infection

Many intestinal E. coli infections can be prevented by measures that interrupt fecal-oral transmission. These include washing hands thoroughly, preventing cross-contamination during food preparation, washing produce appropriately, consuming pasteurized products, and cooking foods such as ground beef to safe temperatures. Safe water supplies and effective sanitation are also essential for preventing transmission.

E. coli in science and biotechnology

Research involving E. coli has contributed substantially to modern understanding of molecular biology and genetics. The insertion of select genes into E. coli plasmids allows for the rapid production of those genes or manufacture the proteins they encode. This process, known as recombinant DNA technology, has numerous applications in research and industry. Genetically engineered E. coli, for example, have been used to produce human insulin and other medically important proteins.