Oral Bacteria Linked to Risk of Stroke

Study looks at hospital cohort

In a study of patients entering a hospital for acute stroke, researchers have increased their understanding of an association between certain types of stroke and the presence of oral cnm-positive Streptococcus mutans. Robert P. Friedland, MD, a professor in neurology at the University of Louisville School of Medicine, co-authored the study, which was published online in Scientific Reports.

In the study, researchers at the National Cerebral and Cardiovascular Center in Osaka, Japan, observed stroke patients to gain a better understanding of the relationship between hemorrhagic stroke and oral bacteria. Among the patients who experienced intracerebral hemorrhage (ICH), 26% were found to have a specific bacterium––cnm-positive S. mutans––in their saliva.

Strokes are characterized as either ischemic strokes, which involve a blockage of one or more blood vessels supplying the brain, or hemorrhagic strokes, in which blood vessels in the brain rupture, causing bleeding.

The researchers also evaluated magnetic resonance imaging (MRI) scans of study subjects for the presence of cerebral microbleeds (CMBs)––small brain hemorrhages that often underlie ICH and that may cause dementia. They found that the number of CMBs was significantly higher in subjects with cnm-positive S. mutans than in those without the bacterium.

The authors hypothesized that S. mutans bacteria may bind to blood vessels weakened by age and hypertension, causing arterial ruptures in the brain, leading to small or large hemorrhages.

“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,” Friedland said. “The study and related work in our labs have shown that oral bacteria are involved in several kinds of stroke, including brain hemorrhages and strokes that lead to dementia.”

Several research studies have shown a close association between the presence of gum disease and heart disease, and a 2013 publication revealed how the bacterium responsible for gum disease worsens rheumatoid arthritis.

Approximately 10% of the U.S. population has oral cnm-negative S. mutans bacteria, which are known to cause tooth decay, Friedland said. He also is researching the role of oral bacteria in other diseases affecting the brain.

“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.

Sources: University of Louisville; February 16, 2016; and Scientific Reports; February 5, 2016.