What is Escherichia coli

E. coli is short for Escherichia coli – a germ that causes severe cramps and diarrhoea and is a leading cause of bloody diarrhoea. The symptoms are worse in children and the elderly, and especially in people who have other illnesses.

The most lethal form of E. coli is E. coli O157:H7 and is an emerging cause of food borne illness. An estimated 73,000 cases of infection and 61 deaths occur in the United States each year. E. coli O157:H7 is one of hundreds of strains of the bacterium Escherichia coli. Although most strains are harmless and live in the intestines of healthy humans and animals, this strain produces a powerful toxin and can cause severe illness.

In the intestine microvilli cover the surface of the epithelial cells. E coli latches on to the surface of an intestinal epithelial cell using long tether like pili. Pili are made of strands of long protein filaments that can adhere to the microvilli on the surface of intestinal cells. Once in contact with the bacterium, the microvilli disappear from a patch of the cell surface, so the bacterium comes into closer contact with the intestinal cell surface, and the next phase in the infection process begins.

The tethered bacterium then uses a specialised injector system to deliver its own proteins into the cell that it is invading. In this case a Type III injector system is used, which is specialised for pumping things into other cells. The bacterium uses the injector system, much like a syringe, to introduce several bacterial proteins into the intestinal cell that force it to cooperate in its own infection.

A needle like tube (purple) called EspA projects from the bacterium to the intestinal cell surface. Two proteins (green) named EspB and EspD travel through the tube to form an opening in the intestinal membrane through which additional bacterial proteins can move into the cell.

With the tube and pore complete, the bacterium then injects a protein called Tir (red) into the cell. The Tir proteins insert themselves into the intestinal cell membrane. A portion of the Tir protein projects beyond the cell surface and binds to a protein on the bacterial cell surface called intimin (blue cups) so that the membranes of the intestinal cell and the bacterium are locked together. The Tir proteins become phosphorylated by intestinal cell proteins (blue balls).

The bacterium is now firmly bound to the intestinal cell surface via the interaction between the Tir and intimin proteins. Pedestal formation then begins. Another intestinal cytoskeletal protein (orange booties) binds to a portion of the bacterial Tir protein that is inside the cell.

Once these proteins bind, long strands of actin (yellow balls) start to form. The actin filaments build up directly beneath where the bacterium is bound to the intestinal cell.

As the actin filaments lengthen, they push the cell membrane upward, and the bacterium becomes perched atop a dramatic pedestal formed by the intestinal cell. Once many enteropathogenic bacteria have adhered to the intestinal lining, symptoms of the infection begin.

How can E. coli infection be caught?

E. coli infection can be caught by doing one of the following:

* Eating undercooked ground beef (the inside is pink)

* Drinking contaminated (impure) water

* Drinking unpasteurised (raw) milk

* Working with cattle

What are the symptoms of E. coli infection?

Symptoms start about 7 days after a person is infected with the germ. The first sign is severe abdominal cramps that start suddenly. After a few hours, watery diarrhoea starts. The diarrhoea causes your body to lose fluids and electrolytes (dehydration). This makes the person feel sick and tired. Then the diarrhoea changes to bright red bloody stools. The infection makes sores in the intestines, so the stools become bloody and the person might have 10 or more bowel movements a day. It also occasionally causes kidney failure.

Are there any complications from E. coli infection?

The most common complication is called haemolytic uremic syndrome. People with this problem get haemolytic anaemia (which is a low red blood cell count), thrombocytopenia (which is a low platelet count) and renal failure (which is kidney damage). Haemolytic uremic syndrome is more common in children and can cause acute renal failure. This problem arises about 5 to 10 days after the diarrhoea starts.

How is the infection treated?

There is no special medication, except drinking a lot of water and watching for complications. Medicine should not be taken to inhibit diarrhoea as it would keep the persons intestines from getting rid of the E. coli germ. If the person is seriously dehydrated, they might need to go to the hospital to have fluids put into their veins with an IV.

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