Commonly abbreviated as 'E. coli', Escherichia coli is a generic term for a large diverse group of bacteria commonly found in the lower intestine of warm-blooded organisms (including mammals and birds) of which most strains are harmless.

The harmless strains are part of the normal flora of the gut, benefiting their hosts by producing vitamin K2, and preventing the establishment of pathogenic bacteria within the intestine.

As a medicine, Nonpathogenic Escherichia coli strain 'Nissle 1917' also known as 'Mutaflor' is used as a probiotic agent for the treatment of various gastroenterological diseases, including inflammatory bowel disease.

While most E. coli strains are harmless, some can cause illness with symptoms including stomach cramps, diarrhea and vomiting, such as serotype O157:H7 which can cause serious food poisoning in humans.

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

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 such as Hemolytic-uremic syndrome. This particular strain is linked to the 2006 United States E. coli outbreak due to fresh spinach.

Certain strains of E. coli, such as O157:H7, O121, O26, O103, O111, O145,and O104:H21, produce potentially lethal toxins and normally these are effectively treated with antibiotics while the 2011 outbreak in Germany represents a new “supertoxic” (HUS) strain of the E.coli bacteria which carries several genes making it resistant to antibiotic treatments and very difficult to treat.

The bacterium latches on to the intestinal wall and produces toxins that cause bloody diarrhoea and, later, haemolytic uraemic syndrome and kidney failure. The consequences can be fatal, but, even for survivors, the long-term consequences are grave. Patients with damaged kidneys need transplants, and damage done to the nervous system may never be reversed.

In 2010, two German toddlers fell victim to a serious E.coli infection. After suffering from bloody diarrhoea and falling into a coma for 10 days, one can no longer walk or talk; the other is blind. The two children are in rehabilitation but will never return to full health.

The bacteria E. coli is a Gram-negative rod-shaped bacterium which can be grown easily in laboratories and its genetics are comparatively simple and easily manipulated or duplicated through a process of metagenics, making it one of the best-studied prokaryotic model organisms, and an important species in biotechnology and microbiology.

E. coli are not always confined to the intestine, and their ability to survive for brief periods outside the body makes them an ideal indicator organism to test environmental samples for fecal contamination.

Regular hand washing, particularly before food preparation or consumption and after toilet contact, is highly recommended, particularly for people who care for small children or are immunocompromised, as the bacterium can be passed from person to person, as well as through food, water and direct contact with animals. As in the 2011 outbreak in Germany, foods are best eaten well cooked with close attention to good kitchen hygiene.

References:
World Health Organisation
Wikipedia
Irish Times