Research has identified a potential link between oral bacteria and the severity of multiple sclerosis (MS), a chronic autoimmune disorder affecting the central nervous system. A study published in the journal Scientific Reports on November 3, 2025, suggests that higher levels of the bacterium Fusobacterium nucleatum in the oral cavity correlate with increased disability in MS patients.
Multiple sclerosis is characterized by inflammation and damage to the myelin sheath, which insulates nerve fibers. The specific causes of MS remain largely unknown, although factors such as viral infections, smoking, vitamin deficiencies, and genetic predispositions may contribute. Notably, the prevalence of MS has risen significantly in Japan since the 1980s, possibly due to environmental changes. While the gut microbiome has been widely studied in relation to MS, the role of oral bacteria has received less attention.
Research Findings on Oral Bacteria and MS
The research team, led by Masahiro Nakamori, an associate professor at Hiroshima University Hospital, examined tongue coating samples from patients with MS and other central inflammatory demyelinating diseases, including neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD). They quantified the periodontal bacterial load, categorizing the relative abundance of Fusobacterium nucleatum as high or low based on its presence in the top 25% of samples.
The study found that patients with a high relative abundance of the bacterium exhibited significantly greater disability, as measured by the Expanded Disability Status Scale (EDSS). Specifically, 61.5% of MS patients with high levels of Fusobacterium nucleatum fell into the moderate-to-severe disability category (EDSS of 4 or greater), compared to only 18.6% of those with milder forms of the disease.
Implications for Understanding Disease Mechanisms
Assistant professor Hiroyuki Naito noted that the association between oral bacteria and disability was not observed in patients with NMOSD or MOGAD, suggesting a unique “oral–brain axis” specific to multiple sclerosis. The researchers adjusted for various clinical factors, including age, disease duration, and MS subtype, and still found that high levels of Fusobacterium nucleatum correlated with nearly tenfold higher odds of severe disability in MS patients.
The findings raise the possibility that Fusobacterium nucleatum may act as a “bridge bacterium,” linking oral inflammation to neurological disability. The research team hopes to expand their studies to confirm these findings across multiple centers and to conduct mechanistic analyses, including cytokine profiling and metagenomic sequencing.
Future research may also explore whether dental interventions, such as periodontal treatment or routine oral care, could influence disease progression in multiple sclerosis. “Ultimately, we aim to clarify how the oral–gut–brain inflammatory axis contributes to multiple sclerosis pathophysiology,” said Naito, emphasizing the need for new strategies in disease modification.
This study highlights the importance of considering oral health as a potentially modifiable factor in understanding and treating multiple sclerosis. The research team includes experts from Hiroshima University’s Department of Clinical Neuroscience and Therapeutics and the Department of General Dentistry.
