We have all considered the mouth-gut barrier as a strong security system. The stomach acid kills the bacteria, viruses, and fungi that we swallow, rendering them senseless and unable to cause us harm. Then what the stomach acid misses the bile salts and enzymes in the small intestine destroy. Perfect protection? Well, maybe not. And if you have any kind of chronic disease or extra inflammation already in the body, definitely not. In this post I’ll describe how oral bacteria travel to the gut, escaping the mouth-gut barrier, and cause inflammation in the lower GI tract. Scientists have really worked overtime in their sleuthing on this one, so it is a bit stunning what they have revealed.
Bad Oral Bacteria = Bad Gut Bacteria
Here’s the basic finding: Bad oral bacteria (germs) get swallowed and colonize further down in the GI tract and wreak havoc on our digestion and absorption of foods, giving rise to leaky gut syndrome, food sensitivities, food allergies, abdominal pain, and disease processes far from the mouth. These germs escape the mouth-gut barrier. What used to be inconceivable has now been proven to be fact.
Does this sound far-fetched? Believe me, at one time it did seem that way to scientists, but as many researchers have diligently carried out careful analysis with the modern sequencing tools that are now available, the picture is becoming clearer. The bacteria in your mouth have a profound impact on gut health, and overall health.
Good bacteria in the mouth equals good bacteria in the gut. Bad or disease-causing bacteria in the mouth equals the same bad bacteria in the gut. Get the picture? Brushing your teeth goes way beyond preventing cavities. Way, way beyond.
- Don’t want abdominal pain? Brush your teeth.
- Don’t want arthritis? Brush your teeth.
- Don’t want heart disease? Brush your teeth.
- Don’t want preterm birth of your precious baby? Brush your teeth.
- Don’t want liver cancer? Pancreatic cancer? Colorectal cancer? Brush your teeth.
Are you starting to hear me?
Now, I am not saying that oral bacteria is the only factor in any of these disease processes. I am also not saying that if you brush your teeth, you have an iron-clad guarantee that these diseases will not be inflicted upon you.
The Mouth: Gateway to Overall Health
What I am saying is that your oral health has a big, usually overlooked, impact on your overall health. Yes, we want to keep our adult teeth until we die, and we don’t want a bunch of holes in them. We don’t want root canals, or implants, or bridges, or dentures. But oral health goes way, way beyond our teeth and gums.
We need to think of our mouths as the gateway to our overall health. You can’t have cavities, gingivitis, periodontitis, candidiasis, or other mouth infections and expect to have great systemic health. You must clean up your gums and teeth to have excellent overall health.
After all, whatever we swallow goes right into our digestive tract. You swallow about 1-1/2 liters of saliva every day, with bacteria in every drop. Do all of the bacteria entering the stomach get deactivated? (Obviously not, for probiotics wouldn’t work if that was the case. Nor would fermented foods like kimchi or sauerkraut be good for you.) So, what if there are potentially pathogenic bacteria in the mouth? Could some of them also survive stomach acid, then bile salts, and then colonize and grow in the small intestine, or even in the large intestine? Let’s look now at what have scientists and researchers found out so far.
Evidence for How Oral Bacteria Travel to the Gut in Sick People
A 2020 review article by Kitamoto and coworkers entitled “The bacterial connection between the oral cavity and the gut diseases” looks at the recent findings of oral bacteria in the gut and their possible contribution to diseases of the gut like irritable bowel syndrome, inflammatory bowel disease, and colorectal cancer. In this article there is a great figure which just lists the names of kinds of oral bacteria that have been found in bloodstream and gut. It is quite a list, which points out the vast number of different bacteria found in bloodstream and gut that appear to be oral bacteria. One of the points from this article is that scientists have found that oral bacteria don’t just stay in the mouth.
The bacteria can travel two basic ways—via the bloodstream (from cuts in the mouth, or dental procedures or severe gum disease or oral cancer) and from swallowing and not being eliminated by the mouth-gut barrier. In there bloodstream there were numerous species from the following genuses: Streptococcus, Staphylococcus, Acinetobacter, Actinomyces, Prevotella, Neisseriaceae, Fusobacteriaceae, Enterobacteriaceae, Pasteurellaceae, and a few others. Oral bacteria in the gut included species from Streptococcus, Staphylococcus, Peptostreptococcaceae, Veillonellaceae, Neisseriaceae, Prevotella, Lactobacillus, Campylobacter, Pasteurellaceae, Aggregatibacter, Porphyromonas gingivalis, Fusobacteriaceae, Enterobacteriaceae, Klebsiella, and a few others. You probably haven’t heard of all of these kinds of bacteria, and neither have I. It is quite a diverse list, and I’m sure it isn’t complete in listing every single strain that is found.
From this figure I gather that oral bacteria don’t stay in the mouth. They travel by the bloodstream or just by swallowing them down into other parts of the body. If the mouth-gut barrier is compromised at all and produces less acid, like when people take proton pump inhibitor drugs, even more oral bacteria get through to the lower intestinal tract.
Focal Infections in the Mouth Contribute to Systemic Disease
A 2022 review article by Peng and coworkers entitled, “Oral microbiota in human systematic diseases,” starts by mentioning the whole concept of focal infections in the mouth from Miller in 1891 and then Frank Billings in early 1900s where they linked oral microbial infections to rheumatoid arthritis, nephritis, endocarditis and other diseases. The idea of “focal infections” was denigrated, denied and ridiculed for many years. But here this article goes into specific detail of the links between oral bacteria and Inflammatory bowel disease, liver diseases (liver cancer, non-alcoholic fatty liver disease, liver cirrhosis), oral cancer, esophageal cancer, pancreatic cancer, colorectal cancer, cardiovascular disease, Alzheimer’s disease, diabetes, rheumatoid arthritis, and preterm birth.
The “foulest four” bacteria are Streptococcus mutans, Fusobacterium nucleatum, Porphyromonas gingivalis, and Streptococcus sanguis, which I have seen mentioned in nearly every publication about nasty oral bacteria which cause systematic damage in the body. The figure below from this article shows the link between oral bacterial and infections in different organs, and diseases affected and covered in this article. Cytokines from the oral infections can send inflammatory signals to the body that give rise to rheumatoid arthritis, diabetes and cardiovascular disease. That is old news now. What is new is that the oral bacteria themselves can travel and colonize where they don’t belong (called ectopic colonization) and directly contribute to cancer, inflammatory bowel disease, Alzheimer’s disease, and preterm birth.
Oral Bacteria and Inflammatory Disease
The 2021 review by Read, Curtis and Neves on “Role of oral bacteria and inflammatory bowel disease,” is notable partly because it is in an influential journal beyond dental journals, Nature Reviews: Gastroenterology & Hepatology. The authors acknowledge the debate about whether disease from nasty oral bacteria comes indirectly from inflammation and cytokines from the oral infections causing disease or whether it comes from translocation of the bacteria themselves. They then put forward an argument for direct translocation of bacteria down into the colon where the ectoptic (out of place) colonization happens.
They proposed a three-stage model for how oral bacteria directly influence IBD. First there is an expansion of the populations of virulent strains of bacteria in the mouth, such as gingivitis or periodontitis, accompanied by a lowered resistance to colonization in the intestinal tract. The second stage is the actual translocation of the oral bacteria into the lower GI tract. Medications like proton pump inhibitors, which lower gastric acid production, could make it easier for bacteria to pass the gastric acid bath in the stomach. Another way to pass into the intestinal tract is by hitchhiking inside of immune cells. There is one kind of T Helper cell 17 (Th17) which is involved in fighting oral infections like periodontitis which also travels via the bloodstream to the intestinal mucosal wall. Fusobacterium nucleatum has been shown to survive inside such immune cells and hitchhike just in this manner. The third and final stage is colonization in the intestinal tract and exacerbation of disease processes. These nasty bacteria caused inflammation in the mouth, and they can do similar damage in the intestinal wall, too. I would show you a picture of the model, but it is behind a paywall, so you have to find it on your own.
Read, Curtis and Neves looked at the transfer of oral bacteria when people are sick, have bad gum disease, compromised mouth-gut barrier, and chronic illness. In such cases the opportunistic pathogenic bacteria in the mouth wreak havoc on the general health of the individual. But what about healthy people? Do oral bacteria get through their mouth-gut barrier?
How Oral Bacteria Travel to the Gut in Healthy People
This question of translocation of oral bacteria in health people was examined exhaustively in a 2019 research paper by Schmidt and coworkers entitled, “Extensive transmission of microbes along the gastrointestinal tract.” This article is really important because it challenges the whole notion of a mouth-gut barrier. This research details the tracking of microbes at the strain level (to make sure it really came from the mouth) not just species level sequencing. A large dataset was used, tracking 310 bacterial species in 470 individuals in 5 countries.
Here is part of what they found:
“We found that transmissions to, and subsequent colonization of, the large intestine by oral microbes is common and extensive among healthy individuals. We found evidence for a vast majority of oral species to be transferable, with increased levels of transmission in colorectal cancer and rheumatoid arthritis patients…”
Schmidt et al, 2019
The authors made a conservative estimate that one in three classifiable salivary microbial cells colonize in the gut and account for 2% of all the bacteria in the large intestine.
“This establishes the oral cavity as an endogenous reservoir for gut microbial strains, and oral-fecal transmission as an important process that shapes the gastrointestinal microbiome in health and disease.”
Schmidt et al, 2019
The research outcomes from this one paper alone are astounding and mind-blowing. The mouth is apparently a continuous source of bacteria for the gut. Whether you have health-promoting or disease-causing bacteria in your mouth will have direct implications on your gut health, and even your overall health. These bacteria get swallowed and many of them survive the passage through the stomach and small intestine.
Transfer of Oral Bacteria to the Gut is a Continuing, Ongoing Process in Health and Disease
The conclusion from all of this research is that, from Schmidt et al especially, microbial transfer from the mouth to the gut is a continuous, ongoing process in health and disease. The bacteria in the mouth play a very significant role in the health of our gut microbiome. This fact is way underappreciated. There is an emphasis on healing the gut, but almost nobody is making the connection between oral health and the gut microbiome. The research results are robust, repeatable, and getting quite convincing.
Bacteria from the mouth are found in many organs throughout the body, not just the gut, and affect a whole host of diseases, and probably others that haven’t been connected yet. The scientific methods available for sequencing bacterial genomes allow strain identification between oral bacterial strains and particular strains found in the gut and elsewhere.
This puts a much greater emphasis on oral health for all of the systemic diseases that people face. Getting the mouth clean is imperative to optimal health. Dental experts for cleaning are great, but a daily routine that is antimicrobial in nature makes a lot of sense. You want a regimen that can clean the gingival pockets and help balance out the kinds of microbes that reside in your mouth. Consider using an essential oil blend like Ora-Shield to help keep your gums clean and healthy and to help balance the microbial population in your mouth. Any disease-causing bacteria are likely to not only cause disease in the mouth, but may have strong effects in the gut and in other organs of the body.
Quick Summary of How Oral Bacteria Travel to the Gut
• Bacteria in your mouth can cause disease in your whole body;
• Many kinds of bacteria from people’s mouths have been found in the bloodstream or lower GI tract;
• Disease-causing bacteria from people’s mouths have been linked to irritable bowel syndrome, inflammatory bowel disease (Crohn’s disease, ulcerative colitis), liver diseases (liver cancer, non-alcoholic fatty liver disease, liver cirrhosis), oral cancer, esophageal cancer, pancreatic cancer, colorectal cancer, cardiovascular disease, Alzheimer’s disease, diabetes, rheumatoid arthritis, and preterm birth;
• Oral bacteria translocation to the gut is far from quack science. Very rigorous analyses have been conducted;
• Healthy people also have at least 2% of their colonic bacteria originate in their mouth;
• Bottom line: Oral bacteria end up in your gut—Are they healthy bacteria or disease-promoting bacteria?
Pingback: What you need to know right now about periodontal disease and diabetes
Pingback: Conquer Gingivitis: The Ultimate Guide To Treat Gingivitis at Home