Escherichia coli

"E. coli" redirects here. See also Entamoeba coli.

Escherichia coli, usually abbreviated to E. coli, discovered by Theodor Escherich, a pediatrician and bacteriologist, is one of the main species of bacteria that live in the lower intestines of mammals. They are necessary for the proper digestion of food and are part of the intestinal flora. Its presence in groundwater is a common indicator of fecal contamination. It belongs among the Enterobacteriaceae, and is commonly used as a model organism for bacteria in general. One of the root words of their family's scientific name, "enteric", refers to the intestine, hence "gastroenteritis" (from 'gastro-', stomach, 'entero-' intestine, '-itis', inflammation). "Fecal" is the adjective for organisms that live in feces, so it is often used synonymously with "enteric".

The number of individual E. coli bacteria in the feces that one human passes in one day averages between 100 billion and 10 trillion. All the different kinds of fecal coli bacteria and all the very similar bacteria that live in the ground (in soil or decaying plants, of which the most common is Enterobacter aerogenes) are grouped together under the name coliform bacteria. Technically, the "coliform group" is defined to be all the aerobic and facultative anaerobic, non-spore-forming, Gram-negative, rod-shaped bacteria that ferment lactose with the production of gas within 48 hours at 35°C (95°F). In the body, this gas is released as flatulence. E. coli cell is elongated, 1-2 µm in length and 0.1-0.5 µm in diameter.

Role in water purification and sewage treatment

In the fields of water purification and sewage treatment, E. coli was chosen very early in the development of the technology as an "indicator" of the pollution level of water, meaning the amount of human fecal matter in it, measured using the Coliform Index. E. coli is used for detection because there are a lot more coliforms in human feces than there are pathogens (such as Salmonella typhi, which causes typhoid), and E. coli is usually harmless, so it can't "get loose" in the lab and hurt anyone. However sometimes it can be misleading to use E. coli alone as an indicator of human fecal contamination because there are other environments in which E. coli grows well, such as paper mills.

Role in disease

Three examples of situations in which the otherwise harmless E. coli can cause illness are:

When the bacteria get out of the intestinal tract and into the urinary tract, they can cause an infection sometimes referred to as "honeymoon cystitis" because intercourse can lead to introduction of bacteria into the bladder. Although it is more common in females, urinary tract infection is seen in both males and females. It is found in roughly equal proportions in elderly men and women. Since bacteria invariably enter the urinary tract through the urethra, poor toilet hygiene can predispose to infection but other factors are also important (pregnancy in women, prostate enlargement in men) and in many cases the initiating event is unclear. Anal sex is also a risk factor.
When the bacteria get out of the intestinal tract through a perforation (a hole or tear, which could be caused by an ulcer, for example) and into the abdomen, they usually cause an infection called "peritonitis" that can be fatal. However, E. coli are extremely sensitive to antibiotics such as streptomycin or gentamycin, so treatment with antibiotics is usually effective.
Certain strains of E.coli such as H7 are toxigenic (some produce a toxin very similar to that seen in dysentery) and can cause food-poisoning usually associated with eating contaminated meat (contaminated during or shortly after slaughter or during storage or display). Severity of the illness varies considerably; it can be fatal, particularly to young children, the elderly or the immunocompromised, but is more often mild. E. coli can harbor both heat-stable and heat-labile enterotoxins. The latter, termed LT, is highly similar in structure and function to Cholera toxin. It contains one 'A' subunit and five 'B' subunits arranged into one holotoxin. The B subunits assist in adherence and entry of the toxin into host intestinal cells, where the A subunit is cleaved and prevents cells from absorbing water, causing diarrhoea.

E. coli can be the causative agent of several intestinal and extra-intestinal infections such as urinary tract infections, meningitis, peritonitis, mastitis, septicemia and gram-negative pneumonia. The enteric E. coli are divided on the basis of virulence properties into enterotoxigenic (ETEC, causative agent of diarrhea in humans, pigs, sheep, goats, cattle, dogs and horses), enteropathogenic (EPEC, causative agent of diarrhea in humans, rabbits, dogs, cats and horses), enteroinvasive (EIEC, found only in humans), verotoxigenic (VTEC, found in pigs, cattle, dogs and cats), enterohaemorragic (EHEC, found in humans, cattle and goats), attaching-effacing (AEEC, collects E. coli found among EPEC in humans, EHEC in humans, cattle and goats, and porcine strains that colonize the gut in a manner similar to human EPEC strains) and enteroaggregative E. coli (EAggEC, found only in humans).

Strains

A "strain" of E. coli is a family with some particular characteristics that make it recognizable from other E. coli strains, the way poodles are recognizable from other strains (or "breeds") of dogs, and different strains of E. coli live in different kinds of animals, so it is possible to tell whether fecal material in water came from humans or from birds, for example. New strains of E. coli arise all the time from the natural biological process of mutation, and some of those strains have characteristics that can be harmful to a host animal. Although in most healthy adult humans such a strain would probably cause no more than a bout of diarrhea, and might produce no symptom at all, in young children, or in people who are or have recently been sick, or in people taking certain medications, an unfamiliar strain can cause serious illness and even death. A particularly virulent example of such a strain of E. coli is H7.

ESBL (Extended-Spectrum Beta-Lactamase) producing E. coli are antibiotic resistant strains of E. coli.ESBL-producing strains are bacteria that produce an enzyme called extended-spectrum beta lactamase, which makes them more resistant to antibiotics and makes the infections harder to treat. In many instances, only two oral antibiotics and a very limited group of intravenous antibiotics remain effective.

Role in microbiology

Because of its ubiquity, E. coli is frequently studied in microbiology and is the current "workhorse" in molecular biology. Its structure is clear, and it makes for an excellent target for novice, intermediate, and advanced students of the life sciences.

Bacterial conjugation was first discovered in E. coli, and E. coli remains the primary model to study conjugation.

E. coli plays an important role in modern biological engineering. Researchers often use the bacteria as "factories" to produce large amounts of DNA and/or proteins. One of the first useful applications of recombinant DNA technology was the manipulation of E. coli to produce human insulin for patients with diabetes.

External links

Model organisms | Enterobacteria

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Role in water purification and sewage treatment

Role in disease

Strains

Role in microbiology

External links