A new study from Hiroshima University suggests that a common oral bacterium, Fusobacterium nucleatum, may be associated with more severe disability in people living with multiple sclerosis (MS). The findings, published in Scientific Reports, add to growing evidence that inflammation originating in the mouth could influence diseases of the central nervous system.
A Possible Oral–Brain Connection
Periodontitis—severe gum disease—has long been known to trigger chronic inflammation and increase the risk of conditions such as diabetes, atherosclerosis, and rheumatoid arthritis. Researchers have also explored how gut bacteria may influence MS, but the role of oral microbes has remained largely unexplored.
The Hiroshima University team set out to change that. They analyzed tongue‑coating samples from patients with MS and two related disorders: neuromyelitis optica spectrum disorder (NMOSD) and MOG‑antibody–associated disease (MOGAD). They measured the relative abundance of several periodontal bacteria and compared these levels with clinical disability scores.
Key Finding: Higher F. nucleatum Levels, Higher Disability
Patients with MS who had high levels of Fusobacterium nucleatum—defined as being in the top 25% of bacterial abundance—were significantly more likely to have moderate to severe disability, measured as an Expanded Disability Status Scale (EDSS) score of 4 or higher.
This association held even after adjusting for age, disease duration, number of relapses, and MS subtype. Nearly two‑thirds of MS patients with high F. nucleatum levels fell into the more disabled category, compared with less than one‑fifth of those with lower levels.
Importantly, the same pattern did not appear in patients with NMOSD or MOGAD, suggesting that the link may be specific to MS.
Researchers also found that MS patients who carried F. nucleatum along with at least one other periodontal pathogen showed even greater disability, hinting at a possible combined effect.
Why This Bacterium Matters
Fusobacterium nucleatum is sometimes called a “bridge bacterium” because it helps connect different microbial communities within dental biofilms. The researchers propose that it might also act as a biological bridge between oral inflammation and neuroinflammatory processes in MS.
Because the mouth is a major source of chronic inflammation—and because oral health is modifiable—the team believes this line of research could open new avenues for prevention or treatment.
The researchers plan to expand their work through larger, multi‑center studies and deeper mechanistic analyses, including cytokine profiling and metagenomic sequencing. They also hope to explore whether improving oral health—through periodontal treatment or routine dental care—could influence MS progression.
Their long‑term goal is to better understand how the oral–gut–brain inflammatory axis contributes to MS and whether targeting oral bacteria could help reduce disability.
