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.

Escherichia coli

Escherichia coli, or E. coli is a bacterium in the family Enterobacteriaceae that is found in the intestines of warm-blooded animals, including humans. E. coli represent about 0.1% of the total bacteria of an adult's intestines (on a Western diet). As part of the normal flora of the human intestinal tract, E. coli aids in food digestion by producing vitamin K and B-complex vitamins from undigested materials in the large intestine and suppresses the growth of harmful bacterial species . However, E. coli has also been linked to diseases in about every part of the body. Pathogenic strains of E. coli have been shown to cause pneumonia, urinary tract infections, wound and blood infections, and meningitis.

Toxin-producing strains of E. coli can cause severe gastroenteritis (hemorrhagic colitis), which can include abdominal pain, vomiting, and bloody diarrhea. In most people, the vomiting and diarrhea stop within two to three days. However, about 5–10% of the those affected will develop hemolytic-uremic syndrome (HUS), which is a rare condition that affects mostly children under the age of 10, but also may affect the elderly as well as persons with other illnesses. About 75% of HUS cases in the United States are caused by an enterohemorrhagic (intestinally-related organism that causes hemorrhaging) strain of E. coli referred to as E. coli O157:H7, while the remaining cases are caused by non-O157 strains. E. coli. O157:H7 is found in the intestinal tract of cattle. In the United States, the Centers for Disease Control and Prevention estimates that there are about 10,000–20,000 infections and 500 deaths annually that are caused by E. coli O157:H7.

E. coli O157:H7, first identified in 1982, and isolated with increasing frequency since then, is found in contaminated foods such as meat, dairy products, and juices. Symptoms of an E. coli O157:H7 infection start about seven days after infection with the bacteria. The first symptom is sudden onset of severe abdominal cramps. After a few hours, watery diarrhea begins, causing lose of fluids and electrolytes (dehydration), which causes the person to feel tired and ill. The watery diarrhea lasts for about a day, and then changes to bright red bloody stools, as the infection causes sores to form in the intestines. The bloody diarrhea lasts for two to five days, with as many as 10 bowel movements a day. Additional symptoms may include nausea and vomiting, without a fever, or with only a mild fever. After about five to 10 days, HUS can develop. HUS is characterized by destruction of red blood cells, damage to the lining of blood vessel walls, reduced urine production, and in severe cases, kidney failure. Toxins produced by the bacteria enter the blood stream, where they destroy red blood cells and platelets, which contribute to the clotting of blood. The damaged red blood cells and platelets clog tiny blood vessels in the kidneys, or cause lesions to form in the kidneys, making it difficult for the kidneys to remove wastes and extra fluid from the body, resulting in hypertension, fluid accumulation, and reduced production of urine. The diagnosis of an E. coli infection is made through a stool culture.

Treatment of HUS is supportive, with particular attention to management of fluids and electrolytes. Some studies have shown that the use of antibiotics and antimotility agents during an E. coli infection may worsen the course of the infection and should be avoided. Ninety percent of children with HUS who receive careful supportive care survive the initial acute stages of the condition, with most having no long-term effects. In about 50% of the cases, short term replacement of kidney function is required in the form of dialysis. However, between 10 and 30% of the survivors will have kidney damage that will lead to kidney failure immediately or within several years. These children with kidney failure require on-going dialysis to remove wastes and extra fluids from their bodies, or may require a kidney transplant.

The most common way an E. coli O157:H7 infection is contracted is through the consumption of undercooked ground beef (e.g., eating hamburgers that are still pink inside). Healthy cattle carry E. coli within their intestines. During the slaughtering process, the meat can become contaminated with the E. coli from the intestines. When contaminated beef is ground up, the E. coli bacteria are spread throughout the meat. Additional ways to contract an E. coli infection include drinking contaminated water and unpasteurized milk and juices, eating contaminated fruits and vegetables, and working with cattle. The infection is also easily transmitted from an infected person to others in settings such as day care centers and nursing homes when improper sanitary practices are used.

Prevention of HUS caused by ingestion of foods contaminated with E. coli O157:H7 and other toxin-producing bacteria is accomplished through practicing hygienic food preparation techniques, including adequate hand washing, cooking of meat thoroughly, defrosting meats safely, vigorous washing of fruits and vegetables, and handling leftovers properly. Irradiation of meat has been approved by the United States Food and Drug Administration and the United States Department of Agriculture in order to decrease bacterial contamination of consumer meat supplies.

The presence of E. coli in surface waters indicates that there has been fecal contamination of the water body from agricultural and/or urban and residential areas. However, the contribution from human vs. agricultural sources is difficult to determine. Since the concentration of E. coli in a surface water body is dependent on runoff from various sources of contamination, it is related to the land use and hydrology of the surrounding watershed . E. coli concentrations at a specific location in a water body will vary depending on the bacteria levels already in the water, inputs from various sources, dilution with precipitation and runoff, and die-off or multiplication of the organism within the water body. Sediments can act as a reservoir for E. coli, as the sediments protect the organisms from bacteriophages and microbial toxicants. The E. coli can persist in the sediments and contribute to concentrations in the overlying waters for months after the initial contamination.

Routine monitoring for enteropathogens, which cause gastrointestinal diseases and are a result of fecal contamination, is necessary to maintain water that is safe for drinking and swimming. Many of these organisms are hard to detect, so monitoring of an indicator organism is used to determine fecal contamination. To provide safe drinking water, the water is treated with chlorine , ultra-violet light, and/or ozone . Traditionally fecal coliform bacteria have been used as the indicator organisms for monitoring, but the test for these bacteria also detects thermotolerant non-fecal coliform bacteria.

Therefore, the U.S. Environmental Protection Agency (EPA) is recommending that E. coli as well as enterococci be used as indicators of fecal contamination of a water body instead of fecal coliform bacteria. The test for E. coli does not include non-fecal thermotolerant coliforms. An epidemiological study has shown that even though the strains of E. coli present in a water body may not be pathogenic, these organisms are the best predictor of swimmingassociated gastrointestinal illness.

The U.S. EPA recreational water quality standard is based on a threshold concentration of E. coli above which the health risk from waterborne disease is unacceptably high. The recommended standard corresponds to approximately 8 gastrointestinal illnesses per 1000 swimmers. The standard is based on two criteria: 1) a geometric mean of 126 organisms per 100 ml, based on several samples collected during dry weather conditions, or 2) 235 organisms/100 ml sample for any single water sample. During 2002, the U.S. EPA finalized guidance on the use of E. coli as the basis for bacterial water quality criteria to protect recreational freshwater bodies.

[Judith L. Sims ]

RESOURCES

BOOKS

Bell, Chris, and Alec Kyriakides. E. coli. Boca Raton: Chapman & Hall, 1998.

Burke, Brenda Lee. Don't Drink the Water: The Waterton Tragedy. Victoria, BC: Trafford Publishing, 2001.

Parry, Sharon, and S. Palmer. E. coli: Environmental Health Issues of Vtec 0157. London, UK:Spon Press, 2001.

Sussman, Max, ed. Escherichia coli: Mechanisms of Virulence. Cambridge, UK: Cambridge University Press, 1997.

U.S. Environmental Protection Agency. Implementation Guidance for Ambient Water Quality Criteria for Bacteria. Draft, EPA-823-B-02-003. Washington, DC: U.S. Environmental Protection Agency, 2002.

PERIODICALS

Koutkia, Polyxeni, Eleftherios Mylonakis, and Timothy Flanigan. "Enterohemorrhagic Escherichia coli : An Emerging Pathogen." American Family Physician, 56, no. 3 (September 1, 1997): 853–858.

OTHER

"Escherichia coli and Recreational Water Quality in Vermont." Bacterial Water Quality. February 7, 2000 [June 2002]. <http://snr.uvm.edu/www/pc/sal/ecoli/index.htm>.

U.S. Food and Drug Administration. "Escherichia coli. " Bad Bug Book. February 13, 2002 [cited May 25, 2002]. <http://vm.cfsan.fda.gov/~mow/chap15.html>.

Escherichia coli

Escherichia coli is one of the most well-known and intensively studied bacteria . Often shortened to E. coli, the bacterium was discovered in 1885 by the German bacteriologist Dr. Theodor Escherich. Initially, the bacterium was termed Bacterium coli, but later the name was changed to honor Dr. Escherich.

Escherichia coli 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.

Escherich was also the first person to demonstrate that the bacterium could cause diarrhea and gastroenteritis (an inflammation of the intestinal tract) in infants. That the bacterium could cause intestinal maladies was at first confusing, given that it exists naturally in the intestinal tract. However, it is now known that certain types of E. coli exist that are more capable of causing disease than other types. If these 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.

E. coli has been a popular bacterium for laboratory research almost since its discovery. This is because the organism can be grown quickly on simple and inexpensive lab growth media. Also, the organism can be used to study bacterial growth in the presence of oxygen (aerobic growth) and in the absence of oxygen (anaerobic growth). The ability of E. coli to grow aerobically and anaerobically classifies the bacterium as a facultative anaerobe.

A type (or strain) of E. coli that has been the workhouse of research is designated K12. K12's biochemical behavior and structure are well known. The huge amount of structural, biochemical, genetic, and behavioral information has made E. coli indispensable as a bacterial model system for numerous studies. Hospital laboratory scientists are also concerned with E. coli, as the bacterium is the primary cause of human urinary tract infections, as well as pneumonia , and traveler's diarrhea.

In its normal habitat of the intestinal tract, E. coli is beneficial. The bacteria participate in the digestion of food, and produce vitamin K and B—complex vitamins.

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 genes 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.

E. coli can be spread to food by handling of the food with unwashed hands, particularly after using the bathroom. The solution to this spread of the bacterium is proper hand washing with soap . Other preventative measures include avoiding unpasteurized milk or apple cider, washing raw foods before consumption, and thorough cooking of ground meat (cattle carcasses can become contaminated with feces during slaughter and the bacterium can be passed on to the ground beef).

The genome sequences of several strains of E. coli have been obtained. The sequence of strain K12 has approximately 4300 protein coding regions making up about 88% of the bacterial chromosome . Most of these proteins function in getting nutrients into the cell . Much of the remainder of the genome is devoted to coding for proteins involved in processing of the nutrients to produce the energy needed for cell survival, growth, and division. The genome sequence of O157:H7 is very different from that of K12. Much of the genome of O157:H7 codes for unique proteins, over 1,300, some of which are necessary for infection. Many of these genes are thought to have been acquired from other microorganisms . Strain O157:H7 is designed to acquire genes and change quickly.

See also Water microbiology; Water treatment.

Resources

books

Donnenberg, M. Escherichia coli: Virulence Mechanisms of a Versatile Pathogen. San Diego: Academic Press, 2002.

Kaper, J.B., and A.D. O'Brien. Escherichia coli O157:H7 andOther Shiga Toxin-producing E.coli Strains. Washington, DC: American Society for Microbiology Press, 1998.

organizations

Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, GA 30333. (404)639–3311. June 20, 2001 [cited November 17, 2002]. <http://www.cdc.gov/ncidod/dbmd/diseaseinfo.escherichiacoli_q.htm.>.

Brian Hoyle

Escherichia Coli

Resources

Escherichia coli is a bacterium, which inhabits the intestinal tract of humansand 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 K-12, 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. Itis 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 bya 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, damageto 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 K-12 in 1997. The genome was discovered to have approximately 4300 protein coding regions making up about 88% of the bacterial chromosome. The most numerous types of proteins were transport and binding proteins—those necessary for the intake of nutrients. A fairly large portion of the genome is reserved for metabolism— the 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 that of K-12, reflecting a common ancestry. But, in contrast to K-12, 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 under gorapid 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.

Resources

BOOKS

Berg, Howard C. E. coli in Motion. New York: Springer,2003.

Donnenberg, M. Escherichia coli : Virulence Mechanisms of a Versatile Pathogen. San Diego: Academic Press, 2002.

Manning, Shannon D., I. Edward Alcamo, and David Heymann. Escherichia coli Infections (Deadly Diseases and Epidemics). New York: Chelsea House Publications, 2004.

Pennington, Hugh. When Food Kills: BSE, E. coli, and Disaster Science. Oxford: Oxford University Press, 2006.

Brian Hoyle

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 K–12, 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 K–12 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 proteins—those necessary for the intake of nutrients. A fairly large portion of the genome is reserved for metabolism—the 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