Clinical trials are underway exploring the potential of oral microbiome transplants—transferring bacteria from the mouths of healthy donors to recipients—as a novel approach to treating various oral health issues, including tooth decay, bad breath, and oral mucositis, a painful inflammation often experienced by cancer patients undergoing chemotherapy or radiotherapy. Researchers are also investigating whether such interventions could eventually help reduce the risk of more serious diseases such as cancer.

The concept builds on growing awareness of the microbiome, the community of microorganisms that inhabit the human body and influence health. While much attention has focused on the gut microbiome, scientists are increasingly recognizing the oral microbiome's important role in systemic health. Healthy oral bacteria form a protective barrier on teeth, gums, and mucosal surfaces, preventing harmful pathogens from colonizing the mouth, entering the bloodstream, and causing inflammation that may contribute to disease.

Dr. Lindsey Edwards, a microbiome scientist at King’s College London, noted that disturbances in the balance of oral bacteria may have broad health implications. Recent studies suggest links between oral microbiome imbalances and conditions ranging from osteoarthritis to bowel cancer and Parkinson’s disease.

A study published in July examined saliva samples from individuals with hand osteoarthritis—an ailment estimated to affect nearly 1.5 million people in the UK—and found elevated levels of the bacterial species Trichococcus, commonly found in sewage, compared to healthy controls. Higher concentrations of this organism correlated with increased joint pain and inflammation, suggesting that immune responses to oral bacteria could contribute to cartilage breakdown.

Additional research has associated variations in oral bacterial profiles with early-onset bowel cancer. Patients diagnosed with the disease showed reduced microbial diversity and distinct bacterial populations compared to healthy individuals. While it remains unclear whether these changes drive cancer development or result from it, researchers propose that saliva testing might offer a non-invasive screening tool for early detection.

King’s College London researchers have also observed differences in oral microbiomes of Parkinson’s disease patients, particularly those who develop dementia—a condition that affects up to half of individuals with Parkinson’s. Their findings indicate that harmful bacteria from the mouth may migrate to the gut, inciting inflammation and potentially contributing to neurodegenerative damage. Lead investigator Frederick Clasen emphasized the need for further study to clarify causality but highlighted the possibility that such bacteria worsen disease outcomes.

The risk posed by pathogenic oral bacteria is not limited to these conditions. If harmful microbes enter the bloodstream through activities such as gum bleeding, they can infect the heart lining, causing infective endocarditis, a potentially fatal complication.

To address these concerns, teams at the University of Washington and Adelaide University are conducting trials to test the efficacy of oral microbiome transplants. At the University of Washington, researchers are targeting halitosis, a condition affecting approximately 25 percent of the British population. Treatment involves creating a saline solution infused with beneficial bacteria extracted from donor saliva, which recipients use as a mouthwash or receive via gum injections to displace odor-causing bacteria. Early results from four participants are expected later this year.

Meanwhile, Australian researchers are investigating whether introducing “good” bacteria can prevent tooth decay by outcompeting harmful bacteria responsible for enamel erosion. Laboratory experiments have identified approximately 250 beneficial oral bacterial species, marking a promising foundation for future interventions.

Experts like Dr. Edwards emphasize that as research progresses, understanding and manipulating the oral microbiome could become as vital to health as managing the gut microbiome, potentially opening new avenues for disease prevention and treatment.