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.
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.
Causes of E. coli 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.
- High fiber diets - researchers from the Uniformed Services University of the Health Sciences reported in the Proceedings of the National Academy of Sciences (PNAS) (May 2013 issue) that people on high fiber diets have a higher risk of harboring E. coli bacteria and suffering the consequences of O157:H7 infection and severe disease. The authors reported that "dietary choice affects Shiga toxin-producing Escherichia coli (STEC) O157:H7 colonization and disease."
Symptoms of E. coli 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 the following symptoms:
- 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.
- 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.
On the next page we look at the risk factors for E. coli infection, complications, diagnosis, prevention and the available treatment options for E. coli infection.