What is E. coli?

What is E. coli?

Our gastrointestinal tract, particularly the colon, is full of many billions of bacteria, with over 500 different species living within us, causing no harm and possibly protecting us from the growth of colonies of other pathogenic bacteria. Escherichia coli (also known as E. coli) is one of these ‘commensal’ bacteria types and we don’t usually know it’s there.

When babies are born their bowels are sterile, but are quickly colonised by bacteria. First by bacteria passed on through contact with their carers skin and mucous membranes, or from the feeding bottle or foods they are fed, or toys they may put in their mouths.

Later we’re colonised by new strains, usually through contaminated food or water, which has been handled by people who haven’t adequately washed their hands after using the toilet or before preparing food.

Strains of E. coli

Every bacteria can be identified genetically and we know it’s only certain strains of E.Coli which can cause problems, usually by the production of toxins.

Most E. coli strains cause no problems at all and are normal residents in the gastrointestinal tract.

Some strains are harmless in the gut but will cause a problem if they migrate to other parts of the body, such as causing urinary tract infection when they are present in the bladder or kidney. It’s unclear how they reach other parts of the body, possibly through the blood stream, but it’s usually through poor hand washing hygiene after going to the toilet and before preparing food, hence the faecal-oral route.

Rarely strains will cause a problem even when just in the gastrointestinal tract. Usually the only symptoms are bloating or diarrhoea, but occasionally certain strains will cause severe kidney or blood disease such as haemolytic-uraemic syndrome (HUS) due to the specific effect of toxins released by the bacteria. These strains may be mutated from previously harmless E. coli.

Outbreaks of serious E. coli infection

Intermittently, outbreaks of E. coli infection occur which are usually new mutations of old strains transmitted through contaminated food.

A recent outbreak in Germany in May 2011 has been ascribed to a new strain of E. coli 0104 called Verocytotoxin- producing E. coli (VTEC) O104 but further testing is occurring to confirm this.

Some strains of E. coli 0104 have been referred to as ‘Shiga-toxin producing E. coli (STEC)’ or Entrohaemorrhagic E. coli (EHEC).

E.coli bacteria
E.coli bacteria

The strain associated with this particular outbreak appears to show an unusual combination of highly virulent properties, prompting scientists to consider it a new strain. DNA testing of bacteria in stool samples from affected patients is being done to ascertain the exact strain and its properties. However, despite initial suspicion around certain vegetable food products (usually sources of E. coli infection are meat products) the source of the new strain and how it has been passed to so many people is still not clear.

Unusually in this outbreak, previously healthy adults seem to be worse affected than the usually more vulnerable groups such as infants and the elderly.

Symptoms of E. coli infection

Simple diarrhoea or bloating and wind may not imply serious infection. However, if you have generalised malaise, fever and diarrhoea, particularly if the diarrhoea is bloody or if you have recently returned from Germany, you should seek medical advice as you’re at higher risk. You will need to supply a stool sample for analysis.

What is haemolytic-uraemic syndrome (HUS)?

Haemolytic-uraemic syndrome (HUS) is usually caused by toxins from an infection, most commonly E. coli, in the digestive system, and the toxins enter the blood stream, poisoning the kidney. Previously, the most common E. coli strain to cause HUS was O157, which was more severe in children and the elderly. Adults can also suffer another disease similar to HUS, called thrombotic thrombocytopenic purpura (TTP), which causes central nervous system involvement.

People who get HUS usually have diarrhoea first, which may be bloody. If you experience bloody diarrhoea, you must seek medical advice.

Although HUS is a serious condition around 98 per cent of people recover. Mortality is higher in the elderly with other underlying health conditions.

Treatment of HUS

Treatment of HUS will depend on how serious the infection is but may include:

*General support such as intra-venous fluids.
*Medications such as corticosteroids.
*Transfusion-packed red blood cells and platelets.
*Plasma filtration or exchange.

Antibiotics aren’t usually used for HUS as they can increase the release of toxin whilst killing the bacteria, magnifying the harm done to the patient’s kidneys. Instead, treatment is generally supportive. Also the current 0104 strain is resistant to several antibiotics, including, unusually for E. coli, cephalosporin type antibiotics.

Prevention of E. coli outbreaks

To prevent the risk of E. coli outbreaks:

Always keep good hygiene, particularly after using the toilet and before preparing food, to prevent the faecal-oral cycle of transmission.
Wash fruit and vegetables to remove excess dirt and therefore reduce bacterial load, although this will probably not remove all bacteria hidden within the surface.
Peeling and cooking fruit and vegetables is more effective at reducing bacterial load.
Location and removal of the source of the infection during an outbreak.