What Is E. Coli? (Escherichia Coli)

Escherichia coli, also known as E. coli is a bacterium that is commonly found in the gut of endotherms (warm blooded organisms).

Several types of E. coli exist as part of the normal flora of the human gut and have many beneficial functions, such as the production of vitamin K2. They also prevent harmful bacteria, known as pathogenic bacteria, from establishing themselves in the intestine.

Most E. coli strains pose no harm to human health, except for serotype O157:H7, which can cause food poisoning in humans and can become life-threatening.

Other less common serotypes, such as O104:H4, O121, O26, O103, O111, O145,and O104:H21 can also cause serious infection.

According to Medilexicon's medical dictionary, Escherichia coli is:

"A species that occurs normally in the intestines of humans and other vertebrates, is widely distributed in nature, and is a frequent cause of infections of the urogenital tract and of neonatal meningitis and diarrhea in infants; enteropathogenic strains (serovars) of Escherichia coli cause diarrhea due to enterotoxin, the production of which seems to be associated with a transferable episome; the type species of the genus."

German pediatrician and bacteriologist, Theodor Escherich discovered the bacterium in 1885, hence its name. E. coli is now classified as part of the Enterobacteriaceae family of gamma-proteobacteria.

A healthy adult will usually make a full recovery from E. coli O157:H7 infection within 5 to 7 days. However, young children, elderly individuals and patients with weakened immune systems can develop potentially fatal HUS (hemolytic uremic syndrome), a type of kidney failure.

E. coli is Gram-negative, facultative anaerobic and non-sporulating. Cells are typically rod-shaped and are about 2 micrometres (μm) long and 0.5 μm in diameter, with a cell volume of 0.6 - 0.7 μm³. It can live on a wide variety of substrates. E. coli uses mixed-acid fermentation in anaerobic conditions, producing lactate, succinate, ethanol, acetate and carbon dioxide. Since many pathways in mixed-acid fermentation produce hydrogen gas, these pathways require the levels of hydrogen to be low, as is the case when E. coli lives together with hydrogen-consuming organisms such as methanogens or sulfate-reducing bacteria. ------------------------------------------------if sulphate reducing bacteria are there the possibilities are high of  E- Coli.

Optimal growth of E. coli occurs at 37°C but some laboratory strains can multiply at temperatures of up to 49°C (we should increase the temp whenever any abnormalities occur in drinking water for better counting). Growth can be driven by aerobic or anaerobic respiration, using a large variety of redox pairs, including the oxidation of pyruvic acid, formic acid, hydrogen and amino acids, and the reduction of substrates such as oxygen, nitrate, dimethyl sulfoxide and trimethylamine N-oxide.^[12]
Strains that possess flagella can swim and are motile. The flagella have a peritrichous arrangement.^[13]
E. coli and related bacteria possess the ability to transfer DNA via bacterial conjugation, transduction or transformation, which allows genetic material to spread horizontally through an existing population. This process led to the spread of the gene encoding shiga toxin from Shigella to E. coli O157:H7, carried by a bacteriophage.

Role as normal flora

E. coli normally colonizes an infant's gastrointestinal tract within 40 hours of birth, arriving with food or water or with the individuals handling the child. In the bowel, it adheres to the mucus of the large intestine. It is the primary facultative organism of the human gastrointestinal tract.^[  As long as these bacteria do not acquire genetic elements encoding for virulence factors, they remain benign commensals.^[

Therapeutic use of nonpathogenic E. coli

Nonpathogenic Escherichia coli strain Nissle 1917 is used as a probiotic agent in medicine, mainly for the treatment of various gastroenterological diseases,^[17] including inflammatory bowel disease.

Role in disease

Virulent strains of E. coli can cause gastroenteritis, urinary tract infections, and neonatal meningitis. In rarer cases, virulent strains are also responsible for hæmolytic-uremic syndrome (HUS), peritonitis, mastitis, septicemia and Gram-negative pneumonia.

Certain strains of E. coli, such as O157:H7, O121 and O104:H21, produce potentially-lethal toxins. Food poisoning caused by E. coli is usually caused by eating unwashed vegetables or undercooked meat. O157:H7 is also notorious for causing serious and even life-threatening complications like hemolytic-uremic syndrome (HUS). This particular strain is linked to the 2006 United States E. coli outbreak of fresh spinach. Severity of the illness varies considerably; it can be fatal, particularly to young children, the elderly or the immunocompromised, but is more often mild. Earlier, poor hygienic methods of preparing meat in Scotland killed seven people in 1996 due to E. coli poisoning, and left hundreds more infected. E. coli can harbor both heat-stable and heat-labile enterotoxins. The latter, termed LT, contains one "A" subunit and five "B" subunits arranged into one holotoxin, and is highly similar in structure and function to Cholera toxins. The B subunits assist in adherence and entry of the toxin into host intestinal cells, while the A subunit is cleaved and prevents cells from absorbing water, causing diarrhea. LT is secreted by the Type 2 secretion pathway

If E. coli bacteria escape the intestinal tract through a perforation (for example from an ulcer, a ruptured appendix, or a surgical error) and enter the abdomen, they usually cause peritonitis that can be fatal without prompt treatment. However, E. coli are extremely sensitive to such antibiotics as streptomycin or gentamicin. This could change since, as noted below, E. coli quickly acquires drug resistance. Recent research suggests that treatment with antibiotics does not improve the outcome of the disease, and may in fact significantly increase the chance of developing haemolytic uraemic syndrome.

Intestinal mucosa-associated E. coli are observed in increased numbers in the inflammatory bowel diseases, Crohn's disease and ulcerative colitis. Invasive strains of E. coli exist in high numbers in the inflamed tissue, and the number of bacteria in the inflamed regions correlates to the severity of the bowel inflammation.

 

Signs and symptoms of E. coli O157:H7 infection

The patient will typically experience symptoms within three to four days after being exposed to the bacteria, however, in some cases they may appear within a day or a week later.

The individual may experience:

• Abdominal pain - typically, the first symptom is severe abdominal cramping that comes on suddenly.
• Diarrhea - a few hours after the sudden abdominal pain, the patient typically has watery diarrhea. A day later there may be bright red bloody stools, caused by sores in the intestines.
• Nausea
• Vomiting - note that many patients who become ill may not vomit
• Fever - note that many infected people may not have a fever
• Fatigue - diarrhea causes loss of fluids and electrolytes (dehydration), making the patient feel sick and tired

A considerable number of infected people have no noticeable symptoms. However, they are capable of unwittingly spreading the infection to others.

What are the causes of E. coli O157:H7 infection?

Most strains of E. coli are harmless. However, one group, including 0157:H7, produces a potent toxin - Shiga toxin - that is harmful for the lining of the small intestine.

Humans can become infected by:

• Ingesting contaminated water - even though tap water contains chlorine and has undergone ozone or ultraviolet treatment, some E. coli outbreaks have been caused by contaminated municipal water supplies. Private wells can be a source of infection, as can some lakes and swimming pools.
• Ingesting contaminated food - examples include ground beef, unpasteurized milk, or fresh vegetables. Infected people who work in restaurants and do not wash their hands properly after going to the toilet can spread the infection to customers and other members of staff.
• Having physical contact with an infected person, known as person-to-person contact. Good hand hygiene is important in stemming the spread of infection.
• Contact with animals - this may not only occur in farms, but also in petting zoos or country fairs.

E. coli infection risk factors

A risk factor is something which raises the chances of developing a condition or disease. For example, obesity significantly raises the risk of developing type 2 diabetes. Therefore, obesity is a risk factor for type 2 diabetes.

The following risk factors are linked to a higher risk of problems with E. coli infection:

• Certain foods - consuming soft cheeses, raw milk, apple juice, cider, and undercooked ground beef are linked to a higher risk of becoming ill
• Immunocompromised patients - those with weakened immune systems, such as patients with AIDS, those taking immunosuppressive medications, and people receiving chemotherapy are susceptible to complications.
• Stomach surgery - patients who have had the size of their stomach surgically reduced have less stomach acid that kills off bacteria.
• The person's age - very young children and elderly individuals have a higher risk of developing serious illness and complications

E. coli infection complications

The vast majority of infected individuals make a full recovery within a week. However, susceptible individuals (mentioned above) may develop hemolytic uremic syndrome (HUS).

Hemolytic uremic syndrome (HUS) - this condition is characterized by hemolysis (breakup of red blood cells) and kidney failure. Platelets, the red blood cells that are responsible for blood clotting, clump together within the small blood vessels of the kidneys, resulting in reduced blood flow (ischemia) and eventually leading to kidney failure. Decreased platelets also increase the risk of bleeding problems.

The patient can develop CNS (central nervous system) problems, including seizures, and can also go into a coma.

Kidney failure among infants and young children is usually caused by HUS.

Patients start off with E. coli infection symptoms - severe abdominal cramps, diarrhea which eventually becomes bloody, and nausea and vomiting (sometimes). While the majority of patients make a full recovery within a week to 10 days, approximately 6% go on to develop HUS. The majority are young children and elderly individuals. Between 3% to 5% of patients with HUS die, according to the National Institutes of Health, USA.

How is E. coli infection diagnosed?

The doctor identifies the signs, asks the patients about symptoms, and sends a stool sample to a lab for analysis.

What are the treatment options for E. coli infection?

No current treatments can cure E. coli O157:H7, it has to run its course.

Most doctors advise patients to get plenty of rest and drink lots of water to prevent dehydration.

The patient should avoid taking OTC medications for diarrhea, as all this will do is slow down the digestive system, undermining the body's ability to eliminate the toxins fast enough.

Prevention

• Cook meat well - especially ground meat.
• Drinks - pasteurized milk, apple juice or cider are safer than unpasteurized.
• Wash vegetables - especially leafy green ones. Washing thoroughly might not protect you completely, but it helps.
• Wash cutlery and crockery - make sure knives, forks, plates and serving dishes are thoroughly washed with warm, soapy water.
• Store foods separately - use separate cutting boards, do not store raw ground beef right next to other foods.
• Hand hygiene - wash your hands thoroughly with warm water and soap after going to the toilet, before preparing foods, after preparing foods, and after touching animals. Wash your hands regularly.

E. coli are friendly bacteria too

E. coli bacteria may also be friendly bacteria, researchers from Cornell University wrote in Nature Chemical Biology (March 25, 2012 issue). The bacterium can produce sugar-modified proteins (glycoproteins) which allow for the production of cheaper and faster pharmaceutical drugs.

The scientists developed a new way of producing human therapeutic glycoproteins by using E. coli as a platform.

Specially designed and genetically engineered proteins are commonly used as medications, because they bind to specific protein receptor sites, and can have therapeutic benefits, such as preventing cancer cells from multiplying.

Written by Christian Nordqvist
Original article date: 21 April 2007. Article updated: 07 November 2012

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