Stroke severity linked to certain strains of gut bacteria

The severity of a stroke and a patient's rate of subsequent recovery have been linked to specific strains of gut bacteria
The severity of a stroke and a patient's rate of subsequent recovery have been linked to specific strains of gut bacteria

Researchers have homed in on several strains of gut bacteria that are associated with the severity of a common form of stroke. The findings build on a growing body of research suggesting future therapies targeting the gut microbiome could reduce a person’s stroke risk, and also aid in their recovery.

The new research, yet to be peer-reviewed and published, was presented at this year’s European Stroke Organisation Conference. Led by Miquel Lledós, from the Sant Pau Research Institute in Spain, the research analyzed a number of fecal samples taken from patients soon after suffering an ischemic stroke.

"In this study we took fecal samples – the first samples taken after the event – from 89 humans who'd suffered an ischemic stroke,” explained Lledós. “Comparing with a control group, we were able to identify multiple groups of bacteria that were associated with a higher risk of ischemic stroke."

The study identified several specific types of bacteria that could be associated with the severity of an acute stroke, including Negativibacillus and Lentisphaeria. Following up on the patients three months later, the study also identified certain bacteria that were associated with functional recovery. In particular the researchers noted a type of bacteria called Acidaminococcus was linked with poor recovery three months after the acute stroke.

"The discovery opens the exciting prospect that in the future, we may be able to prevent strokes or improve neurological recovery by examining the gut microbiota,” said Lledós. “In other pathologies, clinical trials are being carried out where researchers replace the intestinal flora through dietary changes or fecal transplantation from healthy individuals and this should be studied further in the stroke field."

Another new piece of research presented at the conference backed up Lledós’ findings. A Yale University team revealed they identified around 20 types of gut bacteria that could be linked to an increased risk of ischemic stroke.

Cyprien Rivier, a researcher working on the Yale study, said his team’s genetic analysis technique offers insight into the causal relationship between these types of bacteria and stroke. However, the exact mechanisms by which gut bacteria may be influencing stroke risk are still unclear.

“Bacteria can release toxins into the blood, they can also produce certain proteins that interfere with physiological processes,” Rivier explained to The Guardian. “There is also what we call the microbiota-gut-brain axis – a bidirectional pathway between the brain and the microbiome, whereby the brain is influencing the gut through the nerves, and the microbiome is in turn influencing the organs, including the brain, mainly through altering the blood pressure.”

Past research has offered clues to how the gut microbiome could be influencing stroke risk. A key study published last year from the Cleveland Clinic described a link between a metabolite produced by gut bacteria called TMAO (trimethylamine N-oxide) and the severity of stroke.

TMAO is produced in the gut when certain types of bacteria digest animal products such as red meat. In preclinical tests, the Cleveland Clinic research found the severity of stroke was increased when mice were transplanted with high volumes of TMAO-producing gut bacteria.

Interestingly, the relationship between the gut and the brain is likely not a one-way process. Research presented in 2019 found a stroke can directly trigger changes in an animal’s gut microbiome. So while the gut may be influencing the brain, damage in the brain can subsequently have notable effects on the gut.

Source: European Stroke Organization