Escherichia coli (/ˌɛʃəˈrɪkiəˈkoʊlaɪ/ ),[1][2] also known as E. coli (/ˌiːˈkoʊlaɪ/ ),[2] is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms.[3][4] Most E. coli strains are harmless, but some serotypes (EPEC, ETEC etc.) can cause serious food poisoning in their hosts, and are occasionally responsible for food contamination incidents that prompt product recalls.[5][6] Most strains do not cause disease in humans and are part of the normal microbiota of the gut; such strains are harmless or even beneficial to humans (although these strains tend to be less studied than the pathogenic ones).[7] For example, some strains of E. coli benefit their hosts by producing vitamin K2[8] or by preventing the colonization of the intestine by pathogenic bacteria. These mutually beneficial relationships between E. coli and humans are a type of mutualistic biological relationship — where both the humans and the E. coli are benefitting each other.[9][10] E. coli is expelled into the environment within fecal matter. The bacterium grows massively in fresh faecal matter under aerobic conditions for three days, but its numbers decline slowly afterwards.[11]
E. coli and other facultative anaerobes constitute about 0.1% of gut microbiota,[12] and 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.[13][14] A growing body of research, though, has examined environmentally persistent E. coli which can survive for many days and grow outside a host.[15]
The bacterium can be grown and cultured easily and inexpensively in a laboratory setting, and has been intensively investigated for over 60 years. E. coli is a chemoheterotroph whose chemically defined medium must include a source of carbon and energy.[16] E. coli is the most widely studied prokaryotic model organism, and an important species in the fields of biotechnology and microbiology, where it has served as the host organism for the majority of work with recombinant DNA. Under favourable conditions, it takes as little as 20 minutes to reproduce.[17]
E. coli is a Gram-negative, facultative anaerobe, nonsporulating coliform bacterium.[18] Cells are typically rod-shaped, and are about 2.0 μm long and 0.25–1.0 μm in diameter, with a cell volume of 0.6–0.7 μm3.[19][20][21] Antibiotics can effectively treat E. coli infections outside the digestive tract and most intestinal infections but are not used to treat intestinal infections by one strain of these bacteria.[22] The flagella which allow the bacteria to swim have a peritrichous arrangement.[23] It also attaches and effaces to the microvilli of the intestines via an adhesion molecule known as intimin.[24]
E. coli can live on a wide variety of substrates and uses mixed acid fermentation in anaerobic conditions, producing lactate, succinate, ethanol, acetate, and carbon dioxide. Since many pathways in mixed-acid fermentation produce hydrogen gas, these pathways require the levels of hydrogen to be low, as is the case when E. coli lives together with hydrogen-consuming organisms, such as methanogens or sulphate-reducing bacteria.[25]
In addition, E. coli's metabolism can be rewired to solely use CO2 as the source of carbon for biomass production. In other words, this obligate heterotroph's metabolism can be altered to display autotrophic capabilities by heterologously expressing carbon fixation genes as well as formate dehydrogenase and conducting laboratory evolution experiments. This may be done by using formate to reduce electron carriers and supply the ATP required in anabolic pathways inside of these synthetic autotrophs.[26]