A common bacterium normally found in the mouth and digestive system — Streptococcus anginosus — may be more common in the guts of people who have had a stroke, and its presence is linked to worse recovery and a higher risk of death.
These early findings will be presented at the American Stroke Association’s International Stroke Conference 2025.
Researchers in Japan say that one day, a quick test to find harmful bacteria in the mouth or gut could help doctors estimate stroke risk.
If harmful bacteria could be targeted, it might even help prevent strokes.
We all have trillions of bacteria living in our gut and mouth. Most are helpful, aiding digestion and supporting health. But when harmful bacteria become more common than helpful ones, they can cause illness.
The same research team previously found that another bacterium, Streptococcus mutans — known for causing tooth decay — is linked to a higher risk of bleeding in the brain. In this new study, they examined the bacteria in the saliva and stool of people who had recently experienced a stroke and compared them to similar-aged people with no history of stroke.
Key findings:
– Streptococcus anginosus was found much more often in stroke patients than in people without stroke.
– Having this bacterium in the gut was linked to a 20% higher chance of having a stroke, even after accounting for other risk factors.
– Some bacteria were linked to lower stroke risk: Anaerostipes hadrus (18% lower risk) and Bacteroides plebeius (14% lower risk).
– Stroke patients with Streptococcus anginosus had a higher risk of death or major heart and blood vessel problems over the next two years.
The bacteria linked to higher risk, S. mutans and S. anginosus, both contribute to tooth decay. This means good oral hygiene — reducing sugar intake and using toothpaste that targets harmful bacteria — may help protect against stroke.
The study involved 250 Japanese adults, average age 70. Of these, 200 had been diagnosed with a stroke within the past week, and 50 were stroke-free but had routine health checks. Saliva and stool samples were collected and analyzed to measure bacterial levels.
Because the study was done in Japan with a small sample size, the results may not apply to all populations. Lifestyle strongly influences the mix of bacteria in the mouth and gut, so in other countries, different bacteria might play a bigger role.
Experts say these results are intriguing, especially the link between S. anginosus and higher death risk after stroke. More research, especially in people at risk but who haven’t yet had a stroke, could lead to new ways to prevent strokes.
If you care about heart health, please read studies about the stuff in your mouth that can increase heart attack risk and statin alternative lowers risk of heart disease as well as cholesterol levels.
For more about heart health, please read studies that Manganese can help clear arterial plaques and treat heart disease and Aspirin use linked to heart failure.
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