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Escherichia Coli

Escherichia Coli

Definition

E. coli (Escherichia coli) is one of several types of bacteria that normally inhabit the intestine of humans and animals (commensal organism). Some strains of E. coli are capable of causing disease under certain conditions when the immune system is compromised or disease may result from an environmental exposure.

Description

E. coli bacteria may give rise to infections in wounds, the urinary tract, biliary tract, and abdominal cavity (peritonitis ). This organism may cause septicemia, neonatal meningitis, infantile gastroenteritis, tourist diarrhea, and hemorrhagic diarrhea. An E. coli infection may also arise due to environmental exposure. Infections with this type of bacteria pose a serious threat to public health with outbreaks arising from food and water that has been contaminated with human or animal feces or sewage. This type of bacteria has been used as a biological indicator for safety of drinking water since the 1890s. Exposure may also occur during hospitalization, resulting in pneumonia in immunocompromised patients or those on a ventilator

Causes and symptoms

The symptoms of infection and resulting complications are dependent upon the strain of E. coli and the site of infection. These bacteria produce toxins that have a wide range of effects. Symptoms caused by some E. coli infections range from mild to severe, bloody diarrhea, acute abdominal pain, vomiting, and fever. Gastrointestinal complications that can cause E. coli infections include irritable bowel syndrome (IBS) ischemic colitis, appendicitis, perforation of the large bowel, and in some instances gangrene in the colon. Other known E. coli -causing infections may include chronic renal failure, pancreatitis, and diabetes mellitus. Some neurological symptoms such as drowsiness, seizure and coma may occur. In infants, E. coli infections are present in cases of infantile gastroenteritis and neonatal meningitis.

Strains of E. coli that produce diarrhea were initially distinguished by their O (somatic) antigens found on the bacterial surface. Although there is an overlap in characteristics between strains, they may be classified into four main groups; enterohemorrahagic (0157), enteropathogenic (055,0111), enterotoxigenic (06,078), and enteroinvasive (0124,0164).

E.coli O157 (VTEC)

The O157:H7 strain is the member of the group most often associated with a particularly severe form of diarrhea. (The O indicates the somatic antigen, while the H denotes the flagellar antigen, both of which are found on the cell surface of the bacteria.) The bacterium was discovered in 1977, and first reports of infections followed in 1982. E. coli O157:H7, as it is frequently referred to by researchers, causes bloody diarrhea in many infected patients. It accounts for about 2% of all cases of diarrhea in the western world, and at least one-third of cases of hemorrhagic colitis, or about 20,000 cases per year

E. coli O157:H7 is also the most common cause of unique syndromes, known as the Hemolytic-Uremic Syndrome (HUS) and thrombocytopenic purpura (TTP), which causes kidney failure, hemolytic anemia, and thrombocytopenia. Usually, infection with this strain of bacteria will subside without further complications. However, about 5% of people who are infected will develop HUS/TTP. This infection also accounts for the majority of episodes of HUS, especially in children.

This strain of bacteria produces a potent toxin called verotoxin, named for toxin's ability to kill green monkey kidney or "vero" cells. Bacteria that produce verotoxin are referred to as Verotoxin-producing E. coli (VTEC). The numbers of bacteria that are necessary to reproduce infectious levels of bacteria are quite small, estimated at 10-100 viable bacteria. These toxins are lethal for intestinal cells and those that line vessels (endothelial cells), inhibiting protein synthesis causing cell death. It is believed that the damage to blood vessels results in the formation of clots, which eventually leads to the Hemolytic-Uremic Syndrome. HUS/TTP is a serious, often fatal, syndrome that has other causes in addition to E. coli O157:H7; it is characterized by the breaking up of red blood cells (hemolysis) and kidney failure (uremia). The syndrome occurs most often in the very young and very old.

E. coli O157:H7 is commonly found in cattle and poultry, and outbreaks have of disease have been associated with cattle and bovine products. There are reports of contamination from unpasteurized apple juice, hamburger meat, radish sprouts, lettuce, and potatoes, as well as other food sources. Environmental contamination may occur in water drained from cattle pastures or water containing human sewage used for drinking or swimming. Human to human transmission, through contact with fecal matter, has also been identified in daycare centers.

After an incubation period of three to four days on average, watery diarrhea begins, which rapidly progresses to bloody diarrhea in many victims, in which case the bowel movement may be mostly blood. Nausea, vomiting, and low-grade fever are also frequently present. Gastrointestinal symptoms last for about one week, and recovery is often spontaneous. Symptomatic infection may occur in about 10% of infected individuals. About 5-10% of individuals, usually at the extremes of age or elevated leukocyte count, develop HUS/TTP, and ultimately, kidney failure. Patients taking antibiotics or medications for gastric acidity may also be at risk. Neurological symptoms can also occur as part of HUS/TTP and consist of seizures, paralysis, and coma. Rectal prolapse may also be a complication, and in some cases colitis, appendicitis, perforation of the large bowel, and gangrene in the bowel. Systemically, the most prevalent complications of E. coli 157 infections are HUS and TTP.

E. coli non-O157 (VTEC)

These strains of E. coli produce verotoxin, but are strains other than O157. There have been as many as one hundred different types implicated in the development of disease. Strain OH111 was found to be involved in outbreaks in Australia, Japan, and Italy. The O128, O103, and O55 groups have also been implicated in diarrhea outbreaks. In Britain, cases of infantile gastroenteritis in maternity hospitals and neonatal units have been attributed to the E. coli ) non-0157 group. Many of these organisms have been identified in cattle.

Enterotoxigenic E. coli

Two toxins may be produced by this group, the heat-labile enterotoxin (LT) that can produce enteritis in infants, and a heat stable enterotoxin (ST), the action of which has yet to be determined.

Enteroinvasive E. coli

Some strains of the enteroinvasive E. coli have been involved in the development of gastroenteritis in infants. These organisms do not produce and enterotoxin. The cells of the intestine are affected, with the development of symptoms that are typical of a shigellae infection.

Diagnosis

Diagnosis of a specific type of infection is dependant upon the characteristics of the particular strain of the organism.

E. coli O157:H7 (HUS)

This particular strain of E. coli is suspected when bloody diarrhea, bloody stools, lack of fever, elevated leukocyte count, and abdominal tenderness are present. Stool cultures are used to tentatively identify the bacteria. Unfortunately, cultures are often negative or inconclusive if done after 48 hours of symptoms. Further tests are usually needed, however, for confirmation of infection. This may include a full blood count, blood film, and tests to determine urea, electrolyte, and LDH (lactate dehydrogenase) levels. Damaged red blood cells, and elevated levels of creatinine, urea, and LDH with a drop in platelet count may indicate that HUS will develop. Immunomagnetic separation is now being used for diagnosis as well.

E. coli non-O157 (VTEC)

Diagnosis is often difficult for these types of bacteria, but production of enterohemolysin (Ehly) is used as an indicator. Other diagnostic tests are used to detect verotoxins, including ELISA (enzyme-linked immunosorbent assays), colony immunoblotting, and DNA-based tests.

E. coli 0157 STEC

Methods for detection of this type of bacteria are under development, including culture growth media selective for this organism. Immunomagnetic separation and specific ELISA, latex agglutination tests, colony immunoblot assays, and other immunological-based detection methods are being explored.

Treatment

Uncomplicated cases of the E. coli O157:H7 the infection clear up within ten days. It is not certain that antibiotics are helpful in treating E. coli O157:H7 and there is some evidence that they may be harmful. Dehydration resulting from diarrhea must be treated with either Oral Rehydration Solution (ORS) or intravenous fluids. Anti-motility agents that decrease the intestines' ability to contract, should not be used in any patient with bloody diarrhea. Treatment of HUS, if it develops, involves correction of clotting factors, plasma exchange, and kidney dialysis. Blood transfusions may be required. Treatment methods for other E. coli infections are similar. Antibiotics are often used in the treatment of E. coli infections, but their role is controversial. Some antibiotics may enhance the development of HUS/TTP depending upon their action, as well as the use of anti diarrhea medications that should be avoided. Phosphoenolpyruvate analogues may be helpful. Gentamicin, ampicillin, ceftazidime, or beta-lactamase-stable cephalosporin may be administered for neonatal meningitis. Antibiotic therapy is further complicated by the presence of antibiotic resistant organisms.

Alternative treatment

Studies have been conducted to determine if diarrhea symptoms can be reduced by alternative therapies such as the consumption of herbal teas, psyllium, and acupuncture. Patients should consult their doctors before using any alternative treatments, as E. coli can be life threatening and should be closely monitored.

Prognosis

In most cases of O157:H7, symptoms last for about a week and recovery is often spontaneous. Ten percent of individuals with E. coli O157:H7 infection develop HUS; 5% of those will die of the disease. Some who recover from HUS will be left with some degree of kidney damage and possibly irritable bowel syndrome. Additionally, there is a possibility of chronic E. coli infection.

Infants that develop E. coli infections may be permanently affected. Gastroenteritis may leave the child with lactose intolerance. Neonates developing meningitis from E. coli strains have a high morbidity and mortality rate

Prevention

Thorough cooking of all meat and poultry products and adhering to proper food preparation is the most effective way to avoid infection. More studies are needed to determine the appropriate safety margins for killing these bacteria. Food irradiation methods are also being developed to sanitize food. Vaccinations to E. coli 0157 are under development, as are medications aimed at limiting the effects of the verotoxin. The enforcement of regulations for meat production and water are critical. Steam pasteurization is used in the United States and is being explored in other countries.

Prevention of E. coli gastroenteritis in infants is best achieved by breast-feeding. The breast milk contains antibodies that combat the infection. For bottle-fed infants, care should be taken in the preparation of the milk and bottles. Good hygiene of the umbilical cord area is important. Keeping this area clean and dry may reduce infection.

Resources

BOOKS

Shanson, D. C. Microbiology in Clinical Practice. Woburn: Butterworth-Heinemann, 1999.

PERIODICALS

Chart, H., M. Sussman, and D. E. S. Stewart-Tull, eds. "E. coli -Friend or Foe?" Journal of Applied Microbiology TheSociety for Applied Microbiology Symposium Series No. 29.

Long K., E. Vasquez-Garibay, J. Mathewson, J. de la Cabada, and H. DuPont. "The Impact of Infant Feeding Patterns on Infection and Diarrheal Disease Due to Enterotoxigenic Escherichia coli." Salud Publica Mex July-August 1999: 263-70.

OTHER

Centers for Disease Control and Prevention. "Preventing Foodborne Illness: Escherichia coli 0157:H7." August 9, 1996. [cited May 30, 2004]. http://www.cdc.gov/ncidod/dbmd/diseaseinfo/escherichiacoli_g.htm.

KEY TERMS

Antigen A substance, usually a protein, that causes the formation of an antibody and reacts specifically with that antibody.

Anti-motility medications Medications such as loperamide (Imodium), dephenoxylate (Lomotil), or medications containing Codeine or narcotics which decrease the ability of the intestine to contract. This can worsen the condition of a patient with dysentery or colitis.

Colitis Inflammation of the colon or large intestine, usually causing diarrhea that may be bloody.

Food irradiation methods A process using radiant energy to kill microogranisms in food, to extend the amount of time in which food can be sold and eaten safely.

Oral Rehydration Solution (ORS) A liquid preparation developed by the World Health Organization that can decrease fluid loss in persons with diarrhea. Originally developed to be prepared with materials available in the home, commercial preparations have recently come into use.

Urea Chemical formed during the body's metabolism of nitrogen and normally excreted by the kidney. Urea levels rise in the blood when kidney failure occurs.

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Escherichia coli

Escherichia coli

Escherichia coli (E. coli ) is a very common bacterium that normally inhabits the digestive tract of animals, including humans. It is widespread in the natural world and can also be found in soil and water. It is a member of the bacterial family Enterobacteriaciae, which also includes the bacteria Shigella, Salmonella, and Yersinia, among others. Some of these organisms, including E. coli, can cause serious diseases under certain conditions.

Attributes of E. coli

E. coli is important to human health because it is a source of vitamins B12 and K, which it manufactures from undigested food in the large intestine. Unlike many other intestinal bacteria, E. coli can survive and grow in the presence of oxygen (although it can also grow without oxygen), which makes it a useful experimental model organism in the laboratory.

Even though E. coli is a single species of bacteria, many different varieties (called strains) of the species exist. Each has different characteristics, and while some are safe model organisms, others can cause potentially deadly disease. This is the case with E. coli 0157:H7, which is considered a dangerous pathogen which can infect humans. This strain is significantly different from the commonly used laboratory strains, which do not cause disease.

Importance in Laboratory Studies

E. coli is the most well-understood bacterium in the world, and is an extremely important model organism in many fields of research, particularly molecular biology, genetics, and biochemistry. It is easy to grow under laboratory conditions, and research strains are very safe to work with. As with many bacteria, E. coli grows quickly, which allows many generations to be studied in a short time. In fact, under ideal conditions, E. coli cells can double in number after only 20 minutes.

Furthermore, a very large number of E. coli bacteria can be grown in a small spacemany millions in a drop of broth, for example. These are important characteristics in genetic experiments, which often involve selecting a single bacterial cell from among millions of candidates, then allowing it to reproduce into high numbers again to perform additional experiments.

Many vital techniques, such as molecular cloning and overexpression of cloned genes, were initially developed in E. coli and are still simpler and more effective in the bacterium. Crucial experiments that illuminated the details of fundamental biological processes such as DNA replication, transcription , and translation were performed for the first time or with greatest success in E. coli. The bacterium is still a primary resource in many modern laboratories. Even research efforts that focus on other organisms, including humans or crop plants, often use E. coli extensively as a tool to facilitate cloning and DNA sequencing.

Discoveries Made in E. coli

Some of the discoveries made in E. coli have provided an invaluable framework for understanding biological processes in more complex organisms. As mentioned above, many fundamental processes that are shared by all living things are most easily studied in this simple bacterial model. Furthermore,E. coli has served as a model for understanding the biology of other bacteria.

The ways in which E. coli interacts with the human body are in many cases very similar to the ways that other disease-causing organisms act. Therefore, this model organism has been important in the study of human health, and has allowed researchers to ask questions about bacteria in general (for example, how antibiotics stop infections, or how the immune system fights off disease).

Genome Sequenced Early

Sequencing of the E. coli K-12 strain genome (a popular model strain) was completed in 1997; subsequently, at least two collections of the pathogenic 0157:H7 strain have been completely sequenced. The bacterium has a genome of approximately 4.3 million base pairs of DNA, and carries about 4,400 genes. Interestingly, only about 50 percent of the predicted genes have been described and characterized, a surprisingly low percentage for such a well-understood organism. For this and other reasons, E. coli remains one of the most significant model organisms used today.

see also Chromosome, Prokaryotic; Eubacteria; Genome; Human Genome Project; Model Organisms; Plasmid.

Daniel J. Tomso

Bibliography

Madigan, Michael T., John M. Martinko, and Jack Parker. Brock Biology of Micro-organisms, 9th ed. Upper Saddle River, NJ: Prentice Hall, 2000.

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Escherichia coli

Escherichia coli

Escherichia coli is a bacterium, which inhabits the intestinal tract of humans and other warm-blooded mammals. It constitutes approximately 0.1% of the total bacteria in the adult intestinal tract. Its name comes from the name of the person, Escherich, who in 1885 first isolated and characterized the bacterium.

The bacterium, particularly one type called strain K12, is one of the most widely studied organisms in modern research. Its biochemical behavior and structure are well known, having been studied for much of this century. This plethora of information has made E. coli indispensable as the bacterial model system for biochemical, behavioral and structural studies. E. coli is also the most encountered bacterium in clinical laboratories, being the primary cause of human urinary tract infections. Pathogenic (diseases causing) strains of E. coli are responsible for pneumonia , meningitis and traveler's diarrhea.

As part of the normal flora of the intestinal tract, E. coli is beneficial. It is crucial in the digestion of food, and is our principle source of vitamin K and B-complex vitamins. Outside of the intestinal tract, E. coli dies quickly. This trait has been exploited, and E. coli is a popular indicator of drinking water quality , as its presence indicates the recent contamination of the water with feces.

One of the most harmful types of E. coli is a strain called O157:H7. Researchers surmise that O157:H7 arose when an innocuous E. coli bacterium was infected by a virus carrying the genes coding for a powerful toxin called Shiga-like toxin. The toxin can destroy cells in the intestinal tract and, if they enter the bloodstream, can impair or destroy the kidneys and the liver. The intestinal damage causes a lot of bleeding. In children and elderly people, this hemorrhaging can be lethal. In other people, damage to the kidney and liver can be permanent or even lethal. In the summer of 2000, more than 2,000 people in Walkerton, Ontario, Canada were sickened and seven people died from drinking water which had been contaminated with O157:H7.

Strain O157:H7 was first linked to human disease in 1983, when it was shown to have been the cause of two outbreaks of an unusual and severe gastrointestinal ailment in the Unites States. Since then, the number of documented human illnesses and deaths caused by O157:H7 has increased steadily worldwide. Disease caused by E. coli is preventable, by proper hand washing after bowel movements, avoidance of unpasteurized milk or apple cider, washing of raw foods before consumption and thorough cooking of ground meat.

Modern genetics techniques have been successful in obtaining the sequence of the genetic material of E. coli. Frederick Blattner and his colleagues published the genome sequence of strain K12 in 1997. The genome was discovered to have approximately 4300 protein coding regions making up about 88 per cent of the bacterial chromosome. The most numerous types of proteins were transport and binding proteinsthose necessary for the intake of nutrients. A fairly large portion of the genome is reserved for metabolismthe processing of the acquired nutrients into useable chemicals. In 2000, Nicole Perna and her colleagues published the genome sequence of O157:H7. The O157:H7 genome shows similarity to tat of k12, reflecting a common ancestry. But, in contrast to K12, much of the genome of O157:H7 codes for unique proteins, over 1,300, some of which may be involved in disease causing traits. Many of these genes appear to have been acquired from other microorganisms , in a process called lateral transfer. Thus, strain O157:H7 appears to be designed to undergo rapid genetic change. This distinction is important; indicating that strategies to combat problems caused by one strain of E. coli might not be universally successful. Knowledge of the genetic organization of these strains will enable more selective strategies to be developed to combat E.coli infections.

See also Food safety; Microbial flora of the stomach and gastrointestinal tract; Microbial genetics; Waste water treatment; Water purification; Water quality

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Escherichia Coli

Escherichia Coli

Forensic investigations of a food- or water-related outbreak of disease will often focus on select bacteria. One bacterium often associated with contaminated food is Escherichia coli.

Escherichia coli (E. coli ) is one of the most well-known and intensively studied bacteria. It normally inhabits the intestinal tract of humans and other warm-blooded mammals. E. coli constitutes approximately 0.1% of the total bacteria in the adult intestinal tract.

Despite its intestinal habitat, some types (strains) of E. coli cause diarrhea and gastroenteritis (an inflammation of the intestinal tract) in infants. If these more infectious types are present in water or food that is ingested, then an infection can result. The vast majority of the many types of E. coli are harmless to humans.

When E. coli is excreted from the intestinal tract, the bacteria are able to survive only a few hours. This characteristic of rapid death was recognized at the beginning of the twentieth century, when the bacterium began to be used as an indicator of fecal pollution of water. The presence of large numbers of E. coli in water is a strong indicator of recent fecal pollution, and so the possible presence of other intestinal bacteria that cause serious disease (i.e., Vibrio, Salmonella, Shigella). Even today, E. coli remains one of the important tests of water quality.

In 1975, the United States Centers for Disease Control and Prevention identified a new strain of E. coli that was designated O157:H7. Strain O157:H7 was first linked to human disease in 1983, when it was shown to have caused two outbreaks of a severe gastrointestinal illness in the Unites States. This strain is capable of causing severe, even lethal, infection. Those who recover sometimes have permanent kidney damage.

The origin of O157:H7 is not known for certain. The consensus among researchers, however, is that O157:H7 arose when a strain of E. coli living in the intestine and which was not disease causing became infected by a virus. The virus carried the gene coding for a powerful toxin called Shiga-like toxin. Thus, the E. coli acquired the ability to produce the toxin.

The toxin can destroy the cells that line the intestinal tract and can enter the bloodstream and migrate to the kidneys and liver. Severe damage to these organs can occur. The intestinal damage causes severe bleeding, which can be lethal in children and elderly people. During the summer of 2000, E. coli O157:H7 contaminated the drinking water of the town of Walkerton, Ontario, Canada. Over 2,000 people became ill and seven people died. The source of the strain was the intestinal tract of cattle, a known natural habitat of O157:H7.

see also Air and water purity; Bacterial biology; Food supply; Water contamination.

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Escherichia coli

Escherichia coli (ĕsh´ərĬk´ēə kō´lī), common bacterium that normally inhabits the intestinal tracts of humans and animals, but can cause infection in other parts of the body, especially the urinary tract. It is the most common member of the genus Escherichia, named for Theodor Escherich, a German physician. E. coli is a Gram-negative, rod-shaped bacterium propelled by long, rapidly rotating flagella. It is part of the normal flora of the mouth and gut and helps protect the intestinal tract from bacterial infection, aids in digestion, and produces small amounts of vitamins B12 and K. The bacterium, which is also found in soil and water, is widely used in laboratory research and is said to be the most thoroughly studied life form. In genetic engineering it is the microorganism preferred for use as a host for the gene-splicing techniques used to clone genes.

E. Coli Food Poisoning

In 1982 a particularly toxic strain of E. coli,E. coli 0157:H7, was identified; it produces a toxin (Shiga toxin) that damages cells that line the intestines. The same strain was responsible for a 1993 outbreak of food poisoning in Washington state, which sickened 500 people and killed three, and a series of outbreaks in 1996 in Japan, which sickened some 10,000 and killed 12. A rarer and more virulent Shiga-toxin-producing strain, E. coli O104:H4, was the cause of the 2011 outbreak centered on N Germany that sickened more than 4,000 people from more than a dozen countries and killed 50.

Food-poisoning outbreaks due to Shiga-toxin-producing E. coli (STEC) are typically the result of transmission via raw or undercooked ground meat (thought to become contaminated during slaughter or processing) or contaminated salad ingredients. The strains can potentially contaminate any food. STEC infections can also occur through other means, such as contact with infected persons or cattle, or consumption of or contact with contaminated water.

Symptoms, which begin 1 to 8 days after infection and last for about a week, include bloody diarrhea, abdominal pain, vomiting, and in some cases, fever. The most serious complication is a hemolytic-uremic syndrome (HUS) that can lead to kidney failure and death, especially in children. The 2011 infection, for example, led to HUS in some 900 people. There is no treatment other than supportive care. Practical preventive measures include thorough cooking of meat and careful hygiene around infected individuals.

A rapid rise in the number of cases of illness caused by STEC strains has prompted calls for a reevaluation of food inspection techniques in the United States. Irradiation of meat and some greens is now approved by the FDA as a means to destroy such bacteria.

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Escherichia coli

Escherichia coli (E. coli) A species of Gram-negative aerobic bacteria that is found in the intestine (see coliform bacteria) and is also widely used in microbiological and genetics research. The motile rod-shaped cells ferment lactose and are usually harmless commensals, although certain strains are pathogenic and can cause a severe form of food poisoning. Studies of E. coli laboratory cultures have revealed much about the genetics of prokaryotes; the species is also frequently used in genetic engineering, particularly as a host for gene cloning and the expression of recombinant foreign genes in culture.

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Escherichia

Escherichia (family Enterobacteriaceae) A genus of Gram-negative, rod-shaped bacteria. E. coli is the most thoroughly studied of all bacteria. It is found mostly in the lower gut of mammals, but also occurs in, e.g., sewage-contaminated natural waters; it is commonly used as an indicator of sewage pollution. Some strains of E. coli are pathogenic, causing, for example, dysentery in the old and in infants and young animals.

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Escherichia

Escherichia (esh-er-ik-iă) n. a genus of Gram-negative, generally motile, rodlike bacteria that are found in the intestines of humans and many animals. E. coli a species that is usually not harmful but some strains of which cause gastrointestinal infections. E. coli O157 a pathogenic serotype causing colitis, which may give rise to the complications of haemolytic uraemic syndrome or thrombocytopenic purpura.

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