A severe kind of bacteria which causes stomach ulcers could play a role in certain kinds of stroke, researchers suggest.

Specific strains of Helicobacter pylori (H. pylori) were found to be much more prevalent in the blood of patients who had suffered an atherosclerotic stroke.

Atherosclerosis refers to the narrowing and hardening of the arteries because of the build up of fatty deposits.

H. pylori causes ulcers in the stomach.

Researchers from Tor Vergata University in Rome found that strains of the bacteria which produce poisonous cytotoxins can aggravate the risk of arteriosclerosis in large arteries leading to the brain.

Anything that can help to predict the risk of stroke can only be a good thing

Stroke Association spokeswoman

If cytotoxins attack the artery wall, they can cause inflammation and swelling, restricting blood flow and increasing the chance of stroke.

The cytotoxin-asociated gene (CagA) makes strains of H. pylori particularly virulent and damaging to arteries, the researchers say.

Some studies have already linked H. pylori with inflamed artery walls and arterial lesions, including stroke caused by narrowing of the arteries due to atherosclerosis.

Inflammation

The researchers, led by Antonio Piertroiusti, professor of internal medicine at Tor Vergata University, compared different strains of H. pylori in the blood of patients who had had different types of stroke.

One hundred and thirty-eight with a large-vessel stroke, caused by severely narrowed arteries, and 61 with a cardioembolic stroke, caused by a blood clot in the cerebral artery which travels to the brain, were compared with 151 healthy people.

Forty-two per cent of patients who had had large vessel strokes had CagA-positive strains of H. pylori, compared to 19% of those who had cardioembolic strokes.

Only 18% of healthy people in the study had the strains.

The researchers found only CagA-positive strains of H. pylori were associated with ischemic stroke, caused by blockages which restrict blood flow in arteries to the brain. and that this association is confined to patients with atherosclerotic stroke.

Levels of a protein which indicate severe inflammation were also examined.

All stroke patients had higher levels than healthy people, but those with CagA-positive strains of H. pylori had the highest levels of the protein.

The researchers said this showed they had the most severe inflammatory response.

They believe this particular form of H. pylori could increase infection throughout the body, which is known to increase atherosclerosis.

Stroke risk

The team say more research is needed to confirm their findings.

Their study is published in Circulation: Journal of the American Heart Association.

A spokeswoman for the UK Stroke Association said it was a fairly small piece of research.

But she added: "This is an interesting study and we look forward to seeing more research in this area.

"Anything that can help to predict the risk of stroke can only be a good thing. "

"One in four men and one in five women can expect to have a stroke if they live to 85."