There is an association between certain types of stroke and the presence of a specific oral bacteria, according to research carried out by the School of Medicine at the University of Louisville.
The study, published in Scientific Reports (a Nature journal), finds a link between CNM-positive Streptococcus mutans and an increased risk of acute stroke.
Researchers at the National Cerebral and Cardiovascular Centre in Osaka, Japan, observed stroke patients to gain a better understanding of the relationship between haemorrhagic stroke and oral bacteria.
Among the patients who experienced intracerebral haemorrhage, 26 per cent were found to have the bacteria in their saliva. Among patients with other types of stroke, only six per cent tested positive. Haemorrhagic strokes are those in which blood vessels in the brain rupture, causing bleeding. The most common cause is hypertension.
The researchers also looked for the presence of cerebral microbleeds (often a precursor to stroke) in MRI scans. They found that the number of bleeds was significantly higher in subjects with cnm-positive S. mutans than in those without.
The authors believe that the bacteria may bind to blood vessels weakened by age and high blood pressure, causing arterial ruptures in the brain, leading to small or large haemorrhages.
Robert Friedland, professor of neurology at Louisville, said: ‘This study shows that oral health is important for brain health. People need to take care of their teeth because it is good for their brain and their heart as well as their teeth. The study and related work in our labs have shown that oral bacteria are involved in several kinds of stroke, including brain haemorrhages and strokes that lead to dementia.’
The bacteria is found in approximately 10 per cent of the general population, Friedland said, and causes tooth decay.
‘We are investigating the role of oral and gut bacteria in the initiation of pathology in the neurodegenerative disorders Alzheimer’s and Parkinson’s with collaborators in the United Kingdom and Japan,’ he said.
The same bacteria is thought to be a leading cause of endocarditis, a rare and potentially fatal condition in which heart valves are inflamed.
It is believed that the collagen-binding protein CNM helps S. mutans to invade heart tissue.