Advanced, chronic liver disease is estimated to kill over two million people around the world every year. The community of microorganisms in the human gut is thought to be linked to many different health characteristics and conditions, including chronic liver disease. Scientists have also found that another community of microbes, which is in the mouth, may be contributing to this condition when mouth microbes migrate to the gut, and colonize that region.
Now, researchers have shown that there are matching bacterial strains that can be found in both the mouth and gut microbiomes of advanced, chronic liver disease patients. This study has also identified a mechanism through which oral bacteria can influence gut health; it also happens as liver disease gets worse. The findings have been reported in Nature Microbiology.
In this study, the investigators assessed the microbiomes of 86 chronic liver disease patients; they took saliva and stool samples to analyze the microbial populations in the oral and gut microbiomes, respectively. This work indicated that there are significant changes to both the gut and oral microbiomes as liver disease gets worse. Changes in the oral microbiome could even be detected at early stages of disease.
Normally, the oral and gut microbiomes will vary significantly in the same person. But in liver disease patients, those differences began to erode, and they became more similar as disease got worse. Eventually, many bacterial strains in the mouth and guts of patients became nearly identical.
"These strains are typically found in the mouth and are rarely present in the healthy gut. However, we observed increases in the absolute abundances of these oral bacteria in patients with advanced chronic liver disease. This strongly suggests that these bacteria translocate from the mouth and colonize the gut," said co-corresponding study author Melanie Schirmer, Professor of Translational Microbiome Data Integration at the Technical University of Munich (TUM).
There were several oral bacterial species that had moved to grow in patients' guts. As the levels of these bacteria rose, there seemed to be more evidence of damage to the intestinal barrier as well. Further work showed that these bacteria could express enzymes that degrade collagen.
"Collagen breakdown can compromise the gut barrier, potentially allowing bacteria and bacterial products to reach other organs, such as the liver. We believe this may worsen the disease," suggested study co-author Aurelie Cenier, a graduate researcher.
When the microbes from the human patients were grown in a mouse model, there was more damage to the gut barrier and liver fibrosis got worse.
"Our findings open potential new therapeutic strategies for people with advanced chronic liver disease. Protecting or restoring the gut barrier could help slow disease progression. Targeting the oral microbiome offers a way to positively influence the course of the disease and prevent clinical complications," added co-corresponding study author Dr. Vishal Patel of King's College London.
Sources: Technical University of Munich, Nature Microbiology
