Scientists are investigating whether transferring microorganisms from the mouths of healthy people could eventually become a treatment for a range of health problems.
The experimental approach, known as an oral microbiome transplant, involves moving bacteria from a healthy donor into the mouth of someone whose bacterial balance has been disrupted. Although the idea may sound unusual, clinical trials are already examining whether the technique could help with tooth decay, persistent bad breath and oral mucositis.
Oral mucositis is a painful inflammation of the tissues inside the mouth that can develop following cancer treatments such as chemotherapy and radiotherapy.
The Oral Microbiome May Have a Wider Role in Health
The mouth is home to a large community of microorganisms covering the teeth, gums, tongue and the inside of the cheeks.
Many of these bacteria are considered beneficial because they help form a protective barrier against harmful organisms. They can prevent potentially dangerous pathogens from multiplying and entering deeper tissues or the bloodstream.
Dr Lindsey Edwards, a microbiome scientist at King’s College London, believes the oral microbiome could eventually prove to be as important to health as the better-known gut microbiome.
Researchers are increasingly studying whether disturbances in this microbial community may contribute to inflammation and disease elsewhere in the body.
Studies Examine Links Between Mouth Bacteria and Arthritis
Research published in July in RMD Open suggested that changes in the oral microbiome could be associated with osteoarthritis.
Researchers from China, Australia and the UK analysed saliva samples from 52 people with hand arthritis and compared them with samples from healthy individuals.
People with hand arthritis had substantially higher levels of bacteria belonging to the genus Trichococcus. The microorganism is commonly associated with sewage and can colonise the mouth after exposure to contaminated surfaces.
The researchers also found that greater levels of the bacteria were associated with more severe joint pain and inflammation.
One possible explanation is that the immune system responds to bacteria in the mouth, producing chronic, low-level inflammation that could contribute to cartilage damage. However, the findings show an association and do not establish that the bacteria cause arthritis.
Oral Bacteria Are Also Being Studied in Cancer
Scientists are investigating possible connections between oral bacteria and cancer as well.
A study published in BMC Microbiology in July found significant differences in oral bacterial communities between people with early-onset bowel cancer and healthy individuals.
Patients with early-onset bowel cancer had increased levels of certain bacteria and lower overall microbial diversity. Greater diversity is generally considered an important feature of a healthy microbiome.
Researchers have not established whether these bacterial changes contribute to cancer or occur as a consequence of the disease.
However, the findings raise the possibility that saliva could eventually provide a relatively simple way of identifying bacterial patterns associated with bowel cancer, particularly as cases occurring before the age of 50 continue to attract concern.
Parkinson’s Disease Provides Another Clue
Research has also identified differences in the oral microbiome of people living with Parkinson’s disease.
Scientists at King’s College London reported in Gut Microbes last year that Parkinson’s patients who had developed dementia had higher levels of certain potentially harmful bacteria than patients without dementia and healthy participants.
The researchers suggested that some microorganisms may travel from the mouth through the digestive system, where they could contribute to inflammation and the production of substances capable of damaging tissues.
Lead researcher Frederick Clasen cautioned that it remains unclear whether the bacteria contribute directly to cognitive decline or whether changes associated with Parkinson’s disease create conditions that allow particular bacteria to flourish.
Nevertheless, the findings suggest that microorganisms in the mouth could potentially influence the progression of some neurological symptoms.
How Harmful Mouth Bacteria Could Affect Other Organs
According to Dr Edwards, one concern is that bacteria normally found in the mouth can travel to parts of the body where they do not belong.
Some organisms may pass through the digestive system and survive the stomach’s acidic environment before reaching the intestines. Once there, they could interfere with the normal gut microbial balance and stimulate an inappropriate immune response.
Bacteria can also enter the bloodstream through damaged or bleeding gums. In certain circumstances, this can allow microorganisms to reach the heart and infect its inner lining, causing infective endocarditis, a potentially life-threatening condition.
Clinical Trials Are Testing Healthy Saliva
These concerns have prompted researchers to investigate whether introducing beneficial bacteria from healthy donors could restore a healthier microbial balance.
A trial at the University of Washington in the United States is examining whether oral microbiome transplantation could help people with halitosis, or persistent bad breath.
Bad breath commonly occurs when bacteria break down food particles in the mouth and release unpleasant-smelling compounds.
For the experimental treatment, microorganisms are collected from a donor’s mouth and placed into a saline solution. The recipient uses the preparation as a mouthwash, while a more concentrated formulation can be administered directly to the gums.
The researchers hope that beneficial bacteria will compete with and eventually reduce the organisms responsible for the unpleasant odour.
Four patients had received saliva transplants at the time of the report, with results from the wider trial expected later in the year.
Researchers Investigate a Possible New Approach to Tooth Decay
Another research team at the University of Adelaide in Australia is studying whether oral microbiome transplants could help prevent cavities.
Laboratory research identified around 250 types of potentially beneficial bacteria that may help protect teeth by competing with microorganisms responsible for damaging tooth enamel.
The concept is still at an early stage, and further research is required to determine whether the laboratory findings can translate into an effective treatment for people.
Oral Microbiome Research Is Still Developing
Scientists emphasise that oral microbiome transplantation remains experimental. Much of the current evidence demonstrates associations between microbial changes and disease rather than proving that specific bacteria directly cause those conditions.
Even so, researchers believe the field could become increasingly important as scientists learn more about how microorganisms in the mouth interact with the immune system and other organs.
Dr Edwards expects the oral microbiome to become an increasingly significant area of medical research alongside the gut microbiome.
Everyday Ways to Support Oral Bacteria
While microbiome transplantation remains under investigation, basic oral-care habits can help maintain a healthy environment in the mouth.
Regular brushing and daily flossing are among the most important measures because they remove plaque where harmful bacteria can accumulate.
Staying hydrated can also help wash away food particles and sugars that microorganisms use as a source of nourishment.
Diet may play a role as well. Leafy green vegetables such as spinach contain nitrates that can act as prebiotics, supporting certain beneficial bacteria.
Researchers have also raised concerns about frequent use of alcohol-based mouthwashes, which can affect both beneficial and potentially harmful microorganisms. Reducing excessive alcohol consumption may likewise help maintain a healthier microbial balance.
The emerging research does not mean that people should attempt saliva or bacterial transfers themselves. Oral microbiome transplants remain investigational and should only be undertaken within appropriately supervised clinical research.
