For the first time, a new study has found that bacteria common in the mouth has been present in the brains of people who have had a stroke.
Researchers at Tampere University in Finland have found that the cerebral emboli of stroke patients contained DNA from bacteria that came from teeth.
The American Heart Association (AHA) says that embolism occurs when a blood clot or piece of fatty plaque breaks loose and travels through the bloodstream. It is lodged in a blood vessel and blocks blood flow. 
When an embolism blocks the flow of blood to the brain, it is called a cerebral embolism, a type of stroke.
The Tampere University researchers have shown that the cerebral emboli of stroke patients contain DNA from disease-causing oral bacteria.
The research, published May 23 in the Journal of the American Heart Association, involved 75 stroke patients. The samples were studied by duplicating bacterial DNA, showing that 79 percent of the samples contained DNA from oral bacteria.
The study is part of a research project at Tampere University which for 10 years has been investigating the possible association between bacterial infections and the development of cardiovascular disease.
It looked for signs of bacteria in blood clots removed from 75 patients who were treated for an ischemic stroke at Tampere University Hospital between 2013 and 2017.
Ischemic stroke is caused by a blockage in a blood vessel in the brain, accounting for about 87 percent of all strokes.
The Finnish study found that 63 (84 percent) of the study participants had bacterial DNA in their blood clot. Among them, 59 had a strain of streptococci commonly found in the mouth that can cause infections if they get into the bloodstream.
Streptococcus viridans are “normal” bacteria in the mouth. In the oral cavity, streptococci are harmless. But when they enter the blood circulation, they might cause, among other things, infections of the cardiac valves.
“The streptococcus bacteria can directly bind to various platelet receptors, making the patient more prone to blood clots,” Tampere University said in a press statement.
“The research shows that oral health and good dental hygiene are of much greater importance to health than previously known, and that untreated dental infections can cause serious health damage or even death.”
Blood clots in the brain cause 87 percent of strokes.
The work is the first to show common presence of this bacterial DNA in ischemic stroke patients,” said Dr. Olli Patrakka, the study’s lead author. Dr. Patrakka is a graduate student in the Department of Forensic Medicine, Faculty of Medicine and Health Technology, Tampere University.
His colleagues in 2013 found the same strain of streptococci in blood clots removed from patients who had a heart attack. Additional studies found the same bacteria in patients who had a ruptured brain aneurysm or a blood clot in their leg.
Results suggest that bacteria might have a role in the development of serious complications related to atherosclerosis – the buildup of plaque in the arteries, Dr. Patrakka said./WDJ