Escherichia coli

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iEscherichia coli

Conservation status
Secure
Scientific classification
Phylum: Proteobacteria
Class: Gamma Proteobacteria
Order: Enterobacteriales
Family: Enterobacteriaceae
Genus: Escherichia
Species: E. coli
Binomial name
Escherichia coli
T. Escherich, 1885
Low-temperature electron micrograph of a cluster of E. coli bacteria, magnified 10,000 times. Each individual bacterium is oblong shaped.
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Low-temperature electron micrograph of a cluster of E. coli bacteria, magnified 10,000 times. Each individual bacterium is oblong shaped.

Escherichia coli (IPA: [ˌɛ.ʃəˈɹɪ.kjə ˈkʰoʊ.laɪ]), usually abbreviated to E. coli, (coli is Latin for "of the colon") was discovered by Theodor Escherich, a German pediatrician and bacteriologist. It is one of the main species of bacteria living in the lower intestines of mammals, known as gut flora. The number of individual E. coli bacteria in the feces that a human excretes in one day averages between 100 billion and 10 trillion, however the bacteria is not confined to this environment, and specimens have also been located on the edge of hot springs. The E. coli strain O157:H7 is one of hundreds of strains of the bacterium E. coli that causes illness in humans, according to US Department of Health and Human Services Centers for Disease Control and Prevention.

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 cells are elongated, 1–2 µm in length and 0.1–0.5 µm in diameter.

The presence of coliform bacteria in surface water is a common indicator of fecal contamination. E. coli is commonly used as a model organism for bacteria in general. One of the root words of the family's scientific name, "enteric", refers to the intestine, and is often used synonymously with "fecal".

As Gram-negative organisms, E. coli are unable to sporulate. Thus, treatments which kill all active bacteria, such as Pasteurization or simple boiling, are effective for their eradication, without requiring the more rigorous sterilization which also deactivates spores.

As a result of their adaptation to mammalian intestines, E. coli grow best In vivo or at the higher temperatures characteristic of such an environment, rather than the cooler temperatures found in soil and other environments.

Contents

[edit] Role in water purification and sewage treatment

In the field 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 (Salmonella typhi is an example of such a pathogen, causing typhoid fever), 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.

[edit] Role in disease

E. coli can cause 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), enterohaemorrhagic (EHEC, found in humans, cattle and goats), attaching porcine strains that colonize the gut in a manner similar to human EPEC strains) and enteroaggregative E. coli (EAggEC, found only in humans).

The often harmless E. coli can cause illness either by infection of a bodily cavity where it is not normally found, or by synthesis of a toxin which attacks the body. In the first case, the disease can usually be resolved by use of antibiotics which stop the infection, but in the latter case the effects of the toxin persist after the bacteria have been killed. Examples of situations in which E. coli can cause illness are:

  1. When the bacteria travel from the stomach to the intestinal tract, and into the urinary tract, they can cause an infection sometimes referred to as "honeymoon cystitis" because sexual intercourse can lead to introduction of bacteria into the bladder. Although it is more common in females due to the shorter urinary tract, 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 habits 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.
  2. When the bacteria escape the intestinal tract through a perforation (a hole or tear, for example from an ulcer, a ruptured appendix, or a surgical error) and enter the abdomen, they usually cause an infection called "peritonitis" that can be fatal without prompt treatment. However, E. coli are extremely sensitive to antibiotics such as streptomycin or gentamycin, so treatment with antibiotics is usually effective.
  3. Certain strains of E. coli such as Escherichia coli O157:H7 are toxigenic (some produce a toxin very similar to that seen in dysentery) and can cause food poisoning usually associated with eating cheese and contaminated meat (contaminated during or shortly after slaughter or during storage or display). This particular strain is believed to be associated with the 2006 United States E. coli outbreak linked to fresh spinach. 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 diarrhea. LT is secreted by the Type 2 secretion pathway[1]
  4. Since toxigenic coli can be resident in animals which are resistant to the toxin, they may be spread through direct contact on farms, at petting zoos, etc. They may also be spread via airborne particle in such environments.[1]


Appropriate treatment depends on the disease and should be guided by laboratory analysis of the antibiotic sensitivities of the infecting strain of E. coli. As Gram-negative organisms, coli are resistant to many antibiotics which are effective against Gram-positive organisms. Antibiotics which may be used to treat E. coli infection include (but are not limited to) amoxicillin, trimethoprim-sulfamethoxazole, ciprofloxacin, nitrofurantoin. Not all antibiotics are suitable for every disease caused by E. coli, and the advice of a physician should be sought.

Antibiotic resistance is a growing problem. Some of this is due to overuse of antibiotics in humans, but some of it is probably due to the use of antibiotics as growth promoters in food animals.[2]

[edit] Strains

Model of successive binary fission in E. coli
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Model of successive binary fission in E. coli

A "strain" of E. coli is a group with some particular characteristics that make it distinguishable from other E. coli strains. These differences are often detectable only on the molecular level; however, they may result in changes to the physiology or lifecycle of the bacterium, for example leading to pathogenicity. 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 symptoms at all, in young children, 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 E. coli O157:H7.

In addition, E. coli and related bacteria possess the ability to transfer DNA via bacterial conjugation, which allows a new mutation to spread through an existing population. It is believed that this process led to the spread of toxin synthesis from Shigella to E. coli O157:H7.

Extended-Spectrum Beta-Lactamase (ESBL)–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.

[edit] 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. The strains used in the laboratory have adapted themselves effectively to that environment, and are no longer as well adapted to life in the mammalian intestines as the wild type; a major adaptation is the loss of the large quantities of external mucopolysaccharide produced by the wild type in order to protect itself from antibodies and other chemical attacks, but which require a large expenditure of the organism's energy and material resources. This can be seen when culturing the organisms on agar plates; while the laboratory strains produce well defined individual colonies, with the wild type strains the colonies are embedded within this large mass of mucopolysaccharide, making it difficult to isolate individual colonies.

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

Because of this long history of laboratory culture and manipulation, E. coli plays an important role in modern biological engineering. Researchers can alter the bacteria to serve as "factories" to synthesize DNA and/or proteins, which can then be produced in large quantities using the industrial fermentation processes. One of the first useful applications of recombinant DNA technology was the manipulation of E. coli to produce human insulin for patients with diabetes.

[edit] See also

[edit] References

  1. ^ Tauschek M, Gorrell R, Robins-Browne RM,. "Identification of a protein secretory pathway for the secretion of heat-labile enterotoxin by an enterotoxigenic strain of Escherichia coli". PNAS 99: 7066-7071.
  2. ^ Johnson JR, Kuskowski MA,Menard M, et al.. "Similarity between human and chicken Escherichia coli isolates in relation to ciprofloxacin resistance status". J Infect Dis 194: 71–8.

[edit] External links

Major Model Organisms in Genetic Studies
Lambda phage | E. coli | Chlamydomonas | Tetrahymena | Budding yeast | Fission yeast | Neurospora | Maize | Arabidopsis | C. elegans | Drosophila | Zebrafish | Rat | Mouse
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