A preliminary study indicates that a common bacteria typically found in the mouth and gut is more prevalent in individuals who have experienced a stroke.

The research is due to be presented at the American Stroke Association’s International Stroke Conference 2025.

Shuichi Tonomura, the lead author of the study and a physician in the department of neurology at the National Cerebal and Cardiovascular Center in Osaka, Japan, said, “In the future, if there was a quick test to detect harmful bacteria in the mouth and gut, we could use the information to help calculate stroke risk. Targeting these specific harmful oral bacteria may help prevent stroke.”

Bacteria linked to stroke risk

The researchers quantified all detectible bacteria in the saliva and guts of people who had recently had a stroke, comparing them to those without a stroke of similar age undergoing routine medical checkups.

The researchers found that one species of bacteria, Streptococcus anginosus, was significantly more abundant in the saliva and gut of people with acute stroke than in the control group who had not.

An analysis of various groups of bacteria found:

  • Streptococcus anginosus in the gut was independently associated with 20 per cent higher odds of stroke after controlling for vascular risk factors, while Anaerostipes hadrus (a gut bacteria associated with beneficial effects) was associated with a drop in risk by 18 per cent and Bacteroides plebeius was associated with a drop in risk by 14 per cent.
  • Stroke survivors with Streptococcus anginosus in the gut had a significantly higher risk of death and major cardiovascular events over the two-year follow-up period.
  • Increased risk of death and poor outcomes was not noted in stroke survivors with Anaerostipes hadrus and Bacteroides plebeius compared to controls.

Shuichi said, “Our findings offer new insights into the connection between oral bacteria and the risk of stroke, as well as potential strategies for stroke prevention. Both Streptococcus mutans and Streptococcus anginosus are bacteria that contribute to tooth decay by producing acids that break down tooth enamel. This highlights the importance of preventing tooth decay, which can be achieved by reducing sugar intake and using toothpaste that targets these bacteria. Maintaining good oral hygiene is essential.”

The researchers hope to conduct similar studies in people who have not experienced a stroke but have risk factors for stroke.

Shuichi added, “Extending the analysis to populations at risk of stroke is crucial for understanding broader implications and developing potential preventive strategies for those susceptible to stroke.”

Author: