In a recent study conducted in Japan, higher levels of a common bacteria known as Streptococcus anginosus, typically found in the mouth and digestive system, have been linked to a worse prognosis and a heightened risk of mortality in stroke survivors. The findings will be presented at the American Stroke Association’s International Stroke Conference 2025 in Los Angeles, scheduled for February 5-7, 2025, which serves as a premier platform for researchers and healthcare professionals focused on stroke and brain health.
Recent research indicates that Streptococcus anginosus, a bacteria commonly residing in the mouth and gastrointestinal tract, may be more prevalent in the guts of stroke patients, correlating with poorer outcomes and an increased risk of death. This preliminary finding will be showcased at the American Stroke Association’s International Stroke Conference 2025, taking place in Los Angeles on February 5-7. This conference is a leading event for scientists and clinicians devoted to stroke research and brain health.
Shuichi Tonomura, M.D., who led the study and serves as a physician in the neurology department at the National Cerebral and Cardiovascular Center in Osaka, Japan, expressed the potential for quick tests to identify harmful bacteria in the mouth and gut. Such diagnostic tools could aid in predicting stroke risk. “Targeting these particular harmful oral bacteria might help avert stroke occurrences,” he noted.
Our bodies host trillions of bacteria in the gut, referred to collectively as the gut microbiota, alongside another set known as oral microbiota in the mouth. While most of these bacteria contribute positively to bodily functions, including digestion, an imbalance between beneficial and harmful bacteria can lead to health issues, according to Tonomura.
In previous research, the same team identified a different bacterium responsible for tooth decay, Streptococcus mutans, as being associated with an increased risk of bleeding in the brain. In the current study, conducted at Japan’s largest stroke facility, researchers assessed all detectable bacteria present in the saliva and guts of individuals who recently experienced a stroke, comparing them to a control group of similar-aged individuals without a stroke, who were undergoing routine medical examinations.
Findings revealed that Streptococcus anginosus was notably more prevalent in both the saliva and digestive systems of those with acute strokes compared to the control group.
The analysis of various bacterial groups demonstrated:
- Streptococcus anginosus in the gut was independently linked to a 20% greater likelihood of experiencing a stroke, even when considering vascular risk factors. In contrast, Anaerostipes hadrus (a beneficial gut bacterium) was associated with an 18% decrease in stroke risk, while Bacteroides plebeius (common in the Japanese population) corresponded to a 14% reduction in risk.
- During the two-year follow-up, stroke survivors with Streptococcus anginosus in their guts displayed a significantly elevated risk of mortality and major cardiovascular incidents.
- No increased risk of mortality or adverse outcomes was identified in stroke survivors with Anaerostipes hadrus and Bacteroides plebeius when compared to the control group.
“Our results provide valuable insights into the relationship between oral bacteria and stroke risk, along with strategies for prevention,” Tonomura remarked. “Both Streptococcus mutans and Streptococcus anginosus contribute to tooth decay by releasing acids that degrade tooth enamel. This underscores the significance of preventing tooth decay, which can be achieved by lowering sugar consumption and utilizing toothpaste formulated to target these bacteria. Proper oral hygiene is vital,” he emphasized.
The research team aspires to conduct similar studies on individuals who have not suffered a stroke but exhibit stroke risk factors.
“Expanding our analysis to include at-risk populations is critical to comprehending broader implications and developing preventive strategies for those who may experience strokes,” Tonomura stated.
Due to the study being conducted within a Japanese demographic with a relatively limited sample size (189 stroke patients and 55 non-stroke participants), the results may not be entirely applicable to different populations or larger, more diverse groups.
“Lifestyle significantly influences the oral and gut microbiome. Other bacteria might play crucial roles in stroke outcomes in different countries,” Tonomura added.
Louise D. McCullough, M.D., P.H.D., FAHA, who is the Roy M. and Phyllis Gough Huffington Distinguished Chair of Neurology at McGovern Medical School; chief of neurology at Memorial Hermann Hospital-Texas Medical Center; and co-director of UTHealth Neurosciences in Houston, commented on the study’s findings. “The presence of higher levels of Streptococcus anginosus in the guts of recent stroke patients is interesting. Its correlation with increased mortality two years post-stroke may suggest its role in ongoing stroke risk,” she said. “Since this analysis was conducted post-stroke, a broader study involving individuals without stroke but with relevant risk factors could improve our understanding of the connection between these bacteria and stroke risk. This insight could refine prevention strategies.” McCullough also co-authored the commentary titled “Stroke and the Microbiome,” which will appear in the January 2024 edition of the American Heart Association Stroke journal.
Details about the study:
- The research involved 250 participants (average age 70, 40% female, all Japanese). Among them, 200 were diagnosed with a stroke (either hemorrhagic or ischemic) within the last seven days, and 50 individuals of the same age without a stroke history served as controls during routine medical checkups. The control group may also have other medical issues like hypertension, diabetes, or elevated cholesterol levels.
- Stroke patients were treated at Japan’s largest stroke center, the National Cerebral and Cardiovascular Center in Osaka. The control participants were drawn from the ongoing population-based Suita study, which focuses on cardiovascular risk factors in middle-aged and older adults.
- The team analyzed the oral and gut microbiomes using saliva and stool samples collected from stroke patients and control participants between July 2020 and July 2021. They tracked the incidence of mortality and new cardiovascular events among stroke patients over a two-year follow-up period.
