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.
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)
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.
Enterotoxigenic E. coli
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 of a specific type of infection is dependant upon the characteristics of the particular strain of the organism.
E. coli O157
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 0157 STEC
Methods for detection of this type of bacteria are under development, including culture growth media
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.
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.
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
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 anti-bodies 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.
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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 which may be bloody.
Food irradiation methods—A process using radiant energy to kill microogranisms in food, to extend the amount of time in that 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.