More than two million people die every year from advanced chronic liver disease (ACLD). Scientists have known that problems in the gut microbiome—the mix of bacteria in our digestive system—are linked to this disease.
Now, a new study shows that bacteria normally found in the mouth may move to the gut and make the disease worse.
The study, published in Nature Microbiology, looked at saliva and stool samples from 86 people with liver disease. The researchers wanted to know whether bacteria from the mouth could be found in the gut—and what effects this might have.
In healthy people, the types of bacteria in the mouth and gut are usually very different. But in people with advanced liver disease, the researchers found that the bacteria in the mouth and gut started to look more and more alike as the disease worsened. In fact, they found nearly identical strains of bacteria in both places.
“These bacteria are usually only found in the mouth and not in a healthy gut,” said Professor Melanie Schirmer from the Technical University of Munich. “But in patients with serious liver disease, we saw many of them in the gut. This shows they may be moving from the mouth and setting up in the digestive system.”
The researchers then asked how these bacteria might be affecting the body. They discovered that several of the oral bacteria carried special genes that produce enzymes capable of breaking down collagen—a key part of the gut barrier that keeps harmful substances out of the bloodstream.
When these bacteria break down collagen, the gut becomes more “leaky.” This means that bacteria and other harmful substances can pass through the gut wall and reach the liver, potentially making liver disease worse.
To test this, the team isolated the bacteria from human stool samples and showed in the lab that the collagen-breaking enzymes were active. Then, they introduced the bacteria into a mouse model of liver disease. The results were clear: the bacteria made the gut barrier weaker and the liver damage worse.
“We believe that the breakdown of collagen by these bacteria plays a major role in worsening liver disease,” said doctoral researcher Aurelie Cenier, one of the study’s first authors.
This discovery could change how doctors treat and diagnose advanced liver disease. Dr. Vishal Patel from King’s College London said that future treatments could focus on protecting or healing the gut barrier. Another option might be to stop harmful bacteria from moving from the mouth to the gut in the first place.
The researchers also found a possible new way to diagnose the disease earlier. They discovered that the bacterial gene responsible for making the collagen-breaking enzyme was found much more often in people with liver disease than in healthy people. Measuring this gene in stool samples could help doctors spot the disease before it gets worse.
In short, this study shows that bacteria from the mouth can invade the gut, damage the gut lining, and contribute to worsening liver health. These findings could lead to new ways to diagnose, monitor, and treat advanced liver disease by focusing on the role of the microbiome—especially the connection between the mouth and the gut.
If you care about liver health, please read studies about simple habit that could give you a healthy liver, and common diabetes drug that may reverse liver inflammation.
For more information about health, please see recent studies about simple blood test that could detect your risk of fatty liver disease, and results showing this green diet may strongly lower non-alcoholic fatty liver disease.
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