Summary: A recent study indicates that people who have had a stroke are more likely to include the bacteria Streptococcus probiotic in their saliva and gut, which is linked to a higher risk of dying and significant cardiovascular events. Researchers compared 189 stroke patients with 55 non-stroke participants, finding that this bacterium increased stroke risk by 20 %.
In addition, beneficial microorganisms like Bacteroides plebeius and Anaerostipes hadrus were linked to a lower stroke risk. The results highlight the value of oral health in preventing strokes because Streptococcus anginosus causes tooth decay.
Important Facts:
- Stroke Risk Factor: Streptococcus treatment was linked to a 20 % higher injury danger and poorer results.
- Safe Bacteria: Bacteria plebeius and Anaerostipes hadrus were linked to a lower stroke risk.
- Oral Health Connection: Poor oral hygiene may lead to infection, increasing stroke sensitivity.
Origin: AHA
A typical bacteria often found in the mouth and digestive tract,  , Streptococcus anginosis, may be plentiful in the guts of people with , stroke , and is associated with a worse outcome and increased risk of death, according to a preliminary investigation to get presented at the , American Stroke Association’s International Stroke Conference 2025.
The meeting, which will take place in Los Angeles on February 7, 2019, is a top-notch gathering of scientists and clinicians who are passionate about the study of injury and mental health.
If there were rapid tests to find dangerous microbes in the mouth and intestines, we could use the data to compute injury risk in the future.
Shuichi Tonomura, M. D., lead author of the study and staff doctor in the neuroscience section at the National Cerebral and Cardiovascular Center in Osaka, Japan, said,” Targeting these particular dangerous oral bacteria may help reduce injury.”
The gut microbiota, or gut microbiota, are present in every person’s gut, making up trillions of them. Oral microbiota is another type of bacteria that exists in the mouth.
” Most of these bacteria positively affect the body and assist with normal body processes, such as digestion. However, when the helpful and unhelpful types of bacteria get out of balance, illness can happen, Tonomura noted.
Previously, these researchers found that a different bacteria that causes tooth decay,  , Streptococcus mutans, was associated with a higher risk of bleeding inside the brain.
In this brand-new study, which was conducted at the world’s largest stroke center in Japan, researchers compared people who had recently experienced any type of stroke to those who had similar age who were receiving routine medical checks. They also quantified all detectable bacteria in both the saliva and guts.
The researchers discovered that one strain of bacteria, Streptococcus anginosus, was significantly more prevalent in the saliva and gut of those who had experienced an acute stroke than in the control group of people who had not had a stroke.
An analysis of various strains of bacteria revealed:
- Streptococcus anginosus , in the gut was independently associated with 20 % 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 % and Bacteroides , plebeius , ( a gut bacteria common in the Japanese population ) was associated with a drop in risk by 14 %.
- Over the two-year follow-up, 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.
Our findings “offer new insights into the relationship between oral bacteria and the risk of stroke,” as well as potential stroke prevention strategies. By producing acids that break down tooth enamel, both Streptococcus mutans and Streptococcus anginosus are bacteria that contribute to tooth decay.
This emphasizes the value of preventing tooth decay, which can be accomplished by cutting down on sugar intake and applying toothpaste that targets these bacteria. Maintaining good oral hygiene is essential,” Tonomura said.
The researchers intend to conduct similar studies on people who have risk factors for stroke but have not had a stroke.
To understand the full scope of the study and come up with potential preventive measures for those who are at risk of stroke is crucial, according to Tonomura.
The findings may not fully apply to other populations or larger, more diverse groups because the study was conducted in a Japanese population with a relatively small sample size ( 189 stroke patients and 55 non-stroke participants ).
Lifestyle has a significant impact on the gut and oral microbiome. Other bacteria may be main players in stroke in other countries,” Tonomura said.
Poor oral hygiene can cause inflammation and lead to stroke risk. The increased levels of , Streptococcus anginosus , found in the gut of patients with recent stroke is intriguing, and the fact that levels were linked to increased mortality two years after stroke suggests that it may play a role in ongoing stroke risk,” said 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, all in Houston, who was not involved in the study.
Since this study was conducted after a stroke, looking at a larger sample of people who have risk factors but have not yet had a stroke might help us understand how these bacteria are related to stroke risk.
” This knowledge could help improve prevention strategies”. McCullough also coauthored the commentary , Stroke and the Microbiome , published in the Jan. 2024 issue of the American Heart Association Stroke journal.
Study details, background or design:
- The study included 250 people (average age 70, 40 % female, all Japanese ). One hundred patients who had been diagnosed with a stroke (either bleeding or clotting-related ) within the previous seven days were compared to fifty people the same age as them who were receiving a routine medical checkup. The control group may have other medical problems such as high blood pressure, diabetes or high cholesterol.
- The largest stroke center in Japan, the National Cerebral and Cardiovascular Center, was visited by patients with strokes. Controls were participants in the ongoing population-based Suita study, which examines cardiovascular risk factors in middle-aged and older people.
- Between July 2020 and July 2021, researchers used saliva and stool samples collected from stroke patients and controls to examine the oral and digestive microbiomes. Over a two-year follow-up period, they observed how many of the stroke patients died or had new cardiovascular events.
Co-authors, disclosures and funding sources are listed in the manuscript.  ,
About this news from neurology research
Author: Karen Astle
Source: AHA
Contact: Karen Astle – AHA
Image: The image is credited to Neuroscience News
Original Research: The findings will be presented at the 2025 ASA International Stroke Conference.
