Escherichia Coli

Escherichia coli (E. coli) is a gram-negative, rodshaped bacterium. It is one of many types of bacteria (commensal bacteria) that normally inhabit the lower intestine of humans and other warm-blooded animals (commensal organisms). Some strains of E. coli are relatively harmless, but other strains may cause disease in susceptible individuals, particularly the very young, very old, and those with a compromised immune system. The potentially harmful strains of E. coli are transmitted most often through environmental exposure to water and food contaminated by human or animal feces. Foods contaminated with E. coli strains have been responsible for product recalls and infection among large groups of people.

German pediatrician Theodor Escherich (1857–1911) first discovered the Escherichia coli bacterium in 1885 in the feces of healthy individuals. Escherich named the bacterium species Bacterium coli, which was renamed Bacillus coli in 1895 following invalidation of the genus Bacterium. It was renamed to its current species name after the new genus Escherichia was created.

A specific strain of E. coli that produces toxins (Enterotoxigenic E. coli or ETEC) was recognized as a bacterial cause of diarrhea in the 1960s, particularly among travelers and among children in developing countries. Since then it has been recognized as a major cause of foodborne illness in developed countries. Although outbreaks in developed countries have declined through public health efforts, when foodborne illness does occur, enterotoxigenic E. coli is the first bacterium suspected.

E. coli are a diverse group of bacteria, some of which may give rise to infections in wounds, the urinary tract, biliary tract (cholangitis, cholecystitis), and abdominal cavity (peritonitis). Under certain conditions, commensal bacteria overcome the protective responses of their human or animal host and express pathologic (diseasecausing) effects. The pathogenic strains of E. coli may cause illnesses ranging from tourist's diarrhea to more serious illnesses such as hemorrhagic diarrhea (dysentery), septicemia, neonatal meningitis, and infantile gastroenteritis (acute infantile diarrhea). Urinary tract infections (UTI) and vaginal infections are frequently attributed to (E. coli). Exposure to E. coli also may occur during hospitalization, often resulting in pneumonia in immunocompromised patients or those whose breathing is sustained by a mechanical ventilator.

Natural disasters and environmental exposure may result in more widespread E. coli infection. Outbreaks arising from food and water contaminated with human or animal feces or raw sewage can become a serious threat to public health. The presence or absence of E. coli has been used by public health organizations as a biological indicator of water safety since the 1890s.

Enterotoxigenic E. coli serotypes are toxin-forming bacteria that are an important cause of diarrheal illness in humans. Two types of toxin are produced: a heatlabile enterotoxin (LT) that is sometimes responsible for gastroenteritis in infants, and a heat-stable enterotoxin (ST), a toxic amino acid peptide that is found in farm animals such as cattle and sheep. However, although the ST enterotoxin has been found in outbreaks of diarrhea, the relationship between animals carrying a gene for the ST enterotoxin (EAST1) and disease development in humans was as of 2018 not well understood.

After toxin-producing STEC or VTEC bacteria have entered the body, they attach to the mucus membrane lining the intestines and release a toxin (shiga toxin or vero toxin). In turn, the toxins produced by the ETEC subgroup stimulate the intestinal lining to produce excess fluid and the resultant diarrhea. ETEC bacteria include Shiga toxin-producing E. coli (STEC) and verocytotoxin-producing E. coli (VTEC), which are most often associated with foodborne outbreaks. The potent toxin verotoxin is named for the toxin's ability to kill green monkey kidney or vero cells, but even though over 380 VTEC serotypes have been identified, only a few are known to cause disease. ETEC bacteria are transmitted to humans through ingestion of food or water contaminated with animal or human feces. These serotypes cause diarrheal illness, especially in children, and the serotype O157:H7 is the major cause of travelers' diarrhea. In the research laboratory, other STEC serotypes have similar numerical designations representing the O and H antigens (e.g., O157:H7, O26:H11) on the cell surface of the particular bacteria. The O indicates the somatic antigen on the cell surface of gram negative bacterium, and the H denotes a threadlike antigen that is part of the bacterial flagella. The O157:H7 serotype is perhaps the most notable because of its prevalence in outbreaks of foodborne or waterborne illness.

Serotypes in the EHEC subgroup include VTEC and STEC strains that cause bloody diarrhea and hemorrhagic colitis, which can progress to hemolytic uremic syndrome (HUS). HUS comprises three serious clinical conditions appearing at the same time: hemolytic anemia (anemia characterized by destruction of red blood cells), acute kidney failure (uremia), and a low platelet count (thrombocytopenia). It is a gastrointestinal infection that occurs most often in children and, though less frequent in adults, can have high morbidity and mortality. It is sometimes found in combination with shigella and salmonella infections. Among the EHEC subgroup, the dominant serotype is again E. coli O157:H7. However, in 2011, an enteroaggregative Escherichia coli designated as O104:H4 caused a severe outbreak of hemorrhagic colitis and HUS in Europe.

As many as 100 different serotypes of E. coli known as non-O157 have been implicated in the development of disease. Non-O157 shiga toxin-producing E. coli has been responsible for cases of food poisoning. Serotype OH111 was identified in outbreaks in Australia, Japan, and Italy, and serotypes O128, O103, and O55 have also been implicated in diarrhea outbreaks. In the United Kingdom, cases of infantile gastroenteritis in maternity hospitals and neonatal units have been attributed to the STEC non-0157 E. coli) group. Over 380 VTEC non-O157 serotypes have been identified in various foodborne outbreaks.

Some strains of the enteroinvasive E. coli have been identified as the causal bacterium in infantile gastroenteritis. These organisms do not produce an enterotoxin, but they do invade cells in the lining of the intestines, producing symptoms suggestive of shigellosis infection, a type of dysentery.

E. coli may multiply in recreational waters such as ponds, lakes, and public pools. It serves as an indicator of water safety and, when it exceeds a permissible level, allows health officials to warn the public that certain waters are not safe for swimming or drinking. Such warnings sometimes lead to the closing of swimming places until the contamination is controlled. In the United States, levels of E. coli in drinking water are also regulated by the Environmental Protection Agency (EPA) under the Federal Safe Drinking Water Act, a law that protects public drinking water supplies across the country. When levels of the bacterium have exceeded permissible levels in the water supply or in individuals with chronic renal failure or diabetes mellitus of a certain town or city, municipal governments will sometimes issue a boil order for all water used for cooking, drinking, and other in-home uses.

CDC surveillance data gathered through the Emerging Infections Program Foodborne Diseases Active Surveillance Network (FoodNet) indicates that major foodborne infections such as O157 STEC infection and Salmonella infection are not declining and that increased public health efforts are needed to reduce incidence significantly.

Risk factors that affect the susceptibility of individuals to E. coli infection include age, having a weakened immune system, having poor overall health status and/or chronic illness, and eating certain types of foods. Those who are at particularly higher risk include:

In addition to individuals who make up the high-risk population, higher risk of developing E. coli infection is associated with the presence of certain illnesses that create an ideal internal environment for bacterial growth. Chronic gastrointestinal conditions that may increase risk of E. coli infection include irritable bowel syndrome (IBS), inflammatory bowel disease, and colitis.

An E. coli infection is caused by contact with water or food that has been contaminated with feces or through direct contact with the feces of humans or animals. The animals carry the organisms in their intestinal tract and shed them in feces, contaminating soil and water. Humans can become infected by eating underdone meat, animal products, and fresh vegetables and fruit that have come in contact with contaminated water or soil.

Symptomatic infection from E. coli may occur in about 10% of exposed individuals. The symptoms of infection and resulting complications are dependent upon the strain of E. coli, the site of infection, and the overall health status of the individual. After exposure to E. coli and an incubation period of three to four days on average, watery diarrhea begins. The diarrhea may or may not be accompanied by cramping. Most cases with diarrhea resolve in a week or so with rest and maintaining hydration, but in some individuals it may progress rapidly to bloody diarrhea. Nausea, vomiting, and low-grade fever also may be present depending upon the strain and the individual's health status.

Individuals who have a STEC infection usually have stomach cramps, diarrhea, and vomiting, which can range from mild to life-threatening depending on the age and overall health status of the individual. The O157:H7 strain is most often associated with acute bloody diarrhea and is also the most common cause of hemolytic-uremic syndrome (HUS) and thrombocytopenic purpura (TTP). HUS/TTP is a serious syndrome that can progress to kidney failure (uremia), hemolytic anemia (destruction of red blood cells known as hemolysis), thrombocytopenia (low platelet count), and death. Neurologic symptoms such as seizures, paralysis, and coma have also been reported to occur in HUS/TTP. Although most cases of infection with this strain of bacteria subside without further complications, about 5% of people who are infected develop HUS/TTP. The syndrome occurs most often in the very young and very old.

Complications of E. coli infection may include rectal prolapse from continuous diarrhea and, in some cases, ischemic colitis, appendicitis, perforation of the large bowel, and gangrene of the bowel. The most prevalent systemic complications of E. coli O157 infections are HUS and TTP.

Diagnosis of a specific type of infection is dependent upon identifying the particular strain of E. coli responsible. Although laboratory tests are necessary to identify the organism causing illness, the examining physician will gain important clues by considering the patient's age and asking the patient or the parents of a pediatric patient about recent history. The doctor may ask about the household water supply and food preparation habits, recent visits to tropical countries, swimming in a lake or public pool, recent meals taken in a restaurant, whether the child goes to a daycare center regularly, and similar questions. The doctor will also need to know when the patient first noticed the symptoms and how they have progressed.

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. However, cultures are sometimes negative or inconclusive if done after 48 hours of symptoms. Further tests are usually needed to confirm the source of infection. This may include a complete blood count (CBC), blood smear to examine white cells, and biochemistry tests to evaluate blood urea, electrolytes, and LDH (lactate dehydrogenase) levels. Damaged red blood cells and elevated levels of creatinine, urea, and LDH combined with an abnormally low platelet count may indicate possible development of HUS. Other diagnostic tests may detect non-O157 verotoxins, including enzyme-linked immunosorbent assays (ELISA), colony immunoblotting, and DNAbased tests. Culture of a feces sample may reveal that O-157 STEC is the source of infection; culture methods are 85% reliable for identifying 157:H7. Other tests, however, such as immunomagnetic separation, ELISA assays, latex agglutination tests, colony immunoblot assays, and other immunological-based detection methods are subject to individual laboratory protocols and may or may not identify STEC strains. The CDC advises that laboratory procedures must be improved to help protect the public by screening for potentially dangerous E. coli strains.

Uncomplicated cases of E. coli O157:H7 infection typically clear up within ten days. Dehydration resulting from diarrhea is treated with either Oral Rehydration Solution (ORS) or intravenous fluids. Patients with bloody diarrhea are urged not to take any antidiarrheal or anti-motility agents that decrease the intestines' ability to contract (e.g., loperamide, lomotil). Treatment methods for other E. coli infections are similar.

In severe cases in which HUS/TTP develops, treatment may include correcting abnormal clotting factors, plasma exchange, and kidney dialysis. Blood or blood product transfusions are sometimes required.

The use of antibiotics in treating E. coli infection is controversial. Antibiotic therapy may be complicated by the presence of antibiotic resistant organisms that began increasing in the late 1990s and are resistant to penicillins, cephalosporins, fluoroquinolones, and gentamicin, which were previously reserved to treat only the most serious infections. However, treatment with third-generation cephalosporin antibiotics, such as ceftriaxone (Rocephin), is indicated for neonatal meningitis. UTIs may be treated with various antimicrobials, including trimethoprim/sulfamethoxazole (Bactrim DS, Septra), fluoroquinolones such as ciprofloxacin (Cipro), and rifaximin (Xifaxan, RedActive, Flonorm). Most other strains are resistant to antibiotics, including the dominant E. coli O157:H7.

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 die of the disease. Some who recover from HUS are left with a degree of kidney damage and possibly irritable bowel syndrome. Some individuals develop chronic E. coli infection.

Infants who develop E. coli infections may be permanently affected. Gastroenteritis may leave the child with lactose intolerance. Neonates who develop meningitis from E. coli strains have high morbidity and an 8% mortality rate. Some infants may develop neurological and developmental dysfunction.

The CDC recommends following certain precautionary steps routinely in food preparation to minimize the chances of contracting E. coli infection:

Prevention of E. coli gastroenteritis in infants is best achieved by breastfeeding. Breast milk contains antibodies from the mother that help protect the infant against infection. For bottle-fed infants, utmost cleanliness and care are encouraged for preparing the milk or formula and the bottles. Good hygiene of the umbilical cord area is important in newborns. Keeping this area clean and dry may reduce the risk of infection.

In addition to protecting against food sources of infection, the CDC recommends checking out healthy and safe swimming places before going swimming. The CDC has a Healthy Swimming website that provides information about how to enjoy the health benefits of swimming while minimizing risk or illness and injury.

Researchers suggest that more studies are needed to determine the appropriate safety margins for killing harmful bacteria. Although food-irradiation methods are available to sanitize food, not all foods are irradiated, and many people do not want to eat irradiated foods. Steam pasteurization is used in the United States and is being explored in other countries. As of 2018, vaccines against E. coli 0157 were being developed as well as medications aimed at limiting the effects of the shiga toxin in STEC strains.

See also Food contamination ; Food poisoning ; Food safety ; Swimming advisories .