Scientists have discovered the way in which the deadly bacterium E.Coli 0157 kills its victim.

The bug attaches itself to human cells and triggers their own self-destruct mechanism.

Japanese researchers have found that exposing human cells to a molecule called a peptide can protect human cells from harm.

It is hoped that this research could form the basis for new drugs to combat the infection.

The normally harmless E. Coli bacteria encompass potentially deadly versions such as strain 0157 which causes diarrhoea and kidney failure. In developing countries, this strain is responsible for the deaths of nearly one million children and elderly people annually.

Common segment

E. Coli O157:H7, which contaminates cooked meats and other foods, was the particular agent that caused the world's largest outbreak of E.Coli food poisoning in Scotland in 1996 when 20 people died.

In contaminated food, the pathogenic E. Coli secretes molecules called verotoxins, which are then dispersed in the victim's bloodstream. When intestinal, blood, and kidney cells absorb these toxins, they quickly die.

Writing in the journal Genes and Development, Drs Atsushi Suzuki and Hirofumi Doi, and colleagues from several research institutes in Japan, say the verotoxin contains a segment of amino acids called a peptide that is very similar to a sequence in the so-called "suicide" molecule Bcl-2.

The Bcl-2 molecule plays a key role in "programmed cell death" in which damaged cells commit suicide to protect the rest of the organism. This mechanism is one of the body's main defences against tumours.

Synthesised peptide

The Japanese team found that the amino acid sequence that the verotoxin and Bcl-2 have in common is necessary for Bcl-2 to interact with other proteins.

In a sick patient, the verotoxin will attach itself to the outside of a healthy cell using the common segment. This triggers the cell death program in what is otherwise a healthy cell, and organ failure and death will follow unless the toxin is halted.

In an encouraging discovery, the researchers also found that human cells treated with a synthesised copy of the peptide before exposure to the verotoxin came to no harm.

It is hoped that this information about how E.Coli 0157 causes human cells to self-destruct could form the basis for new drugs to treat the infection.