Stroke strikes 795,000 Americans each year and kills 130,000, according to the Centers for Disease Control and Prevention. Of the survivors, many are left with permanent disabilities, both physical and mental. But what if the bacteria in your gut could influence the severity of a stroke, or whether you even had one in the first place?

Researchers at Weill Cornell Medicine have found that bacteria found in the gut could decrease the severity of a stroke.

For their study, scientists gave mice a combination of antibiotics. Two weeks later, they induced ischemic strokes in mice, the most common type of stroke in which blocked blood vessels keep blood from reaching the brain.

The size of the stroke was 60 percent smaller in mice that received the antibiotics than the animals that didn't receive the medication. According to the researchers, microbes in the gut guided the immune cells to protect the brain, and shielded it from the stroke's full impact.

"Our experiment shows a new relationship between the brain and the intestine," said Dr. Josef Anrather, an associate professor of neuroscience at Weill Cornell Medicine. "The intestinal microbiota shape stroke outcome, which will impact how the medical community views stroke and defines stroke risk."

The findings suggest that modifying microbes in the gut can be a way to prevent stroke. It could be especially useful to high-risk patients, like those undergoing cardiac surgery or those who have multiple obstructed blood vessels in the brain.

Although scientists don't understand which types of bacteria were protective, they do know that the bacteria did not interact with the brain chemically, but instead modified the behavior of immune cells. Immune cells from the gut found their way to the outer coverings of the brain, called the meninges, where they organized and directed a response to the stroke.

"One of the most surprising findings was that the immune system made strokes smaller by orchestrating the response from outside the brain, like a conductor who doesn't play an instrument himself but instructs the others, which ultimately creates music," said Dr. Costantino Iadecola, a professor of neurology at Weill Cornell Medicine.

The study gives hope that stroke could be prevented by changing the dietary habits of patients at risk.

"Dietary intervention is much easier to accomplish than drug use, and it could reach a broad base," Dr. Anrather said.

However, treating or preventing stroke by changing the bacteria in the gut is still in the future. "It's music of the future," said Anrather. "But diet has the biggest effect of composition of microbiota, and once beneficial and deleterious species are identified, we can address them with dietary intervention."

The study was published in the journal Nature Medicine.