The bacteria that cause violent diarrhoea among people travelling in the developing world may not be a such a bad thing after all.

Scientists believe that the bug, E. coli, may also protect against colon and bowel cancer.

The idea that a bacterial product could lead to inhibition of colon cancer growth is very exciting indeed Professor Emad El-Omar

Colorectal cancer is a leading cause of cancer-related death in the developed world, where E. coli infection is less common.

But conversely in the developing world, where E. coli infection is much more common, colorectal cancer is not the killer that it is in industrialised nations.

Researchers decided to examine whether this meant that E. coli was in some way helping to protect against the development of cancer.

Toxin

They focused on the effect of a particular toxin produced by the bacterium on colon cancer cells.

They found that when the toxin was added to a culture of cancer cells their rate of division slowed markedly.

The defining quality of cancer cells is that they divide in an uncontrolled way, and do not stop dividing as healthy cells do at the end of their life.

Further tests showed that the E. coli toxin mimics the effects of two chemicals - guanylin and uroguanylin - that control colorectal cell division.

Cells exposed to the toxin had a much longer cell cycle, and hence divided at a much lower rate than cells that did not receive the toxin.

The researchers, from Thomas Jefferson University, Philadelphia, and the Mayo Clinic, Rochester, hope their finding will make it possible to develop new drugs to treat colorectal cancer by exploiting the same pathway targeted by E. coli toxins to stem cell division.

Important function

Professor Emad El-Omar, a gastroenterology expert from the University of Aberdeen and expert adviser to Colon Cancer Concern said bacteria in the colon performed many useful functions.

He said: "There is evidence that these bacteria control many physiological functions that are very important in health and disease."

Professor El-Omar said the concept of an in-balance of "beneficial" and "harmful" bacteria pre-disposing the host to serious disease was not new.

But he said: "The idea that a bacterial product (a toxin in this case) could lead to inhibition of colon cancer growth is very exciting indeed.

"I think this line of research has a great potential for uncovering novel mechanisms of disease, and in time novel therapeutic approaches."

The research is published in the Proceedings of the National Academy of Sciences.