E Coli
For the protozoan parasite, see Entamoeba coli.
Binomial name
Escherichia coli
(Migula 1895)
Castellani and Chalmers 1919
Escherichia coli (commonly E. coli; pronounced /ˌɛʃɪˈrɪkiə ˈkoʊlaɪ/, /iː ~/), is a bacterium that is commonly found in the lower intestine of warm-blooded animals.
coli strains are harmless, but some, such as serotype O157:H7, can cause serious food poisoning in humans, and are occasionally responsible for costly product recalls. The harmless strains are part of the normal flora of the gut, and can benefit their hosts by producing vitamin K2, or by preventing the establishment of pathogenic bacteria within the intestine.
E. coli are not always confined to the intestine, and their ability to survive for brief periods outside the body makes them an ideal indicator organism to test environmental samples for fecal contamination. The bacteria can also be grown easily and its genetics are comparatively simple and easily-manipulated, making it one of the best-studied prokaryotic model organisms, and an important species in biotechnology.
coli was discovered by German pediatrician and bacteriologist Theodor Escherich in 1885, and is now classified as part of the Enterobacteriaceae family of gamma-proteobacteria.
Strains
Model of successive binary fission in E. coli is a sub-group within the species that has unique characteristics that distinguish it from other E.
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, a strain may gain pathogenic capacity, the ability to use a unique carbon source, the ability to inhabit a particular ecological niche or the ability to resist antimicrobial agents.
coli strains are present in a water sample, for example, assumptions can be made about whether the contamination originated from a human, other mammal or bird source.
New strains of E. coli evolve through the natural biological process of mutation, and some strains develop traits that can be harmful to a host animal.
Although virulent strains typically cause no more than a bout of diarrhea in healthy adult humans, particularly virulent strains, such as O157:H7 or O111:B4, can cause serious illness or death in the elderly, the very young or the immunocompromised.
Biology and biochemistry
Escherichia coli cells use long, thin structures called flagella to propel themselves. These flagella form bundles that rotate counter-clockwise, creating a torque that causes the bacterium to rotate clockwise.
E.
The cells are about 2 micrometres (μm) long and 0.5 μm in diameter, with a cell volume of 0.6 - 0.7 μm3. It can live on a wide variety of substrates. coli normally colonizes an infant's gastrointestinal tract within 40 hours of birth, arriving with food or water or with the individuals handling the child.
It is the primary facultative organism of the human gastrointestinal tract. As long as these bacteria do not acquire genetic elements encoding for virulence factors, they remain benign commensals.
Role in disease
Virulent strains of E. In rarer cases, virulent strains are also responsible for hæmolytic-uremic syndrome (HUS), peritonitis, mastitis, septicemia and Gram-negative pneumonia..
coli and certain other foodborne illnesses can sometimes trigger serious health problems months or years after patients survived that initial bout.
Virulence properties
Enteric E. coli (ETEC): causative agent of diarrhea (without fever) in humans, pigs, sheep, goats, cattle, dogs, and horses.
ETEC uses fimbrial adhesins (projections from the bacterial cell surface) to bind enterocyte cells in the small intestine. ETEC can produce two proteinaceous enterotoxins: the larger of the two proteins, LT enterotoxin, is similar to cholera toxin in structure and function, while the smaller protein, ST enterotoxin causes cGMP accumulation in the target cells and a subsequent secretion of fluid and electrolytes into the intestinal lumen.
ETEC strains are non-invasive, and they do not leave the intestinal lumen. ETEC is the leading bacterial cause of diarrhea in children in the developing world, as well as the most common cause of traveler's diarrhea.
Each year, ETEC causes more than 200 million cases of diarrhea and 380,000 deaths, mostly in children in developing countries.
Enteropathogenic E. EPEC lack fimbriae, ST and LT toxins, but they utilize an adhesin known as intimin to bind host intestinal cells.
Adherence to the intestinal mucosa causes a rearrangement of actin in the host cell, causing significant deformation. EIEC infection causes a syndrome that is identical to Shigellosis, with profuse diarrhea and high fever.
EIEC are highly invasive, and they utilize adhesin proteins to bind to and enter intestinal cells. It uses bacterial fimbriae for attachment, is moderately-invasive and possesses a phage-encoded Shiga toxin that can elicit an intense inflammatory response.
Enteroaggregative E.
So named because they have fimbriae which aggregate tissue culture cells, EAggEC bind to the intestinal mucosa to cause watery diarrhea without fever. coli are usually associated with eating unwashed vegetables and meat contaminated post-slaughter.
O157:H7 is further notorious for causing serious and even life-threatening complications like hemolytic-uremic syndrome (HUS). The latter, termed LT, contains one 'A' subunit and five 'B' subunits arranged into one holotoxin, and is highly similar in structure and function to Cholera toxins.
coli are observed in increased numbers in the inflammatory bowel diseases, Crohn's disease and ulcerative colitis. Invasive strains of E. coli often occurs via fecal-oral transmission. Common routes of transmission include: unhygienic food preparation, farm contamination due to manure fertilization, irrigation of crops with contaminated greywater or raw sewage, feral pigs on cropland, or direct consumption of sewage-contaminated water. Dairy and beef cattle are primary reservoirs of E.
Because women have a shorter urethra than men, they are 14-times more likely to suffer from an ascending UTI.
Uropathogenic E. The organism is lysine positive, and grows on TSI slant with a (A/A/g+/H2S-) profile.
There exist three protocols for diagnosis:
(a) Diagnosis is carried out as is the case with EPEC and ETEC.
(b) Gram stain:- G - ve, rods, with no particular arrangement. coli is "on the order of 10–5 per genome per generation, which is 1,000 times as high as previous estimates," a finding which may have significance for the study and management of bacterial antibiotic resistance.
Antibiotic-resistant E.
In many instances, only two oral antibiotics and a very limited group of intravenous antibiotics remain effective.
Increased concern about the prevalence of this form of "superbug" in the United Kingdom has led to calls for further monitoring and a UK-wide strategy to deal with infections and the deaths. Susceptibility testing should guide treatment in all infections in which the organism can be isolated for culture.
Phage therapy
Phage therapy—viruses that specifically target pathogenic bacteria—has been developed over the last 80 years, primarily in the former Soviet Union, where it was used to prevent diarrhea caused by E.