Summary: High levels of the periodontal bacteria Fusobacterium nucleatum may be associated with more severe disability in people with multiple sclerosis. The researchers analyzed samples of the tongue layer and found that MS patients with higher abundance of this bacteria had significantly worse scores on a standard disability scale.
The effect appeared specific to MS and was not observed in two other demyelinating diseases, suggesting a possible MS-specific oral-brain inflammatory pathway. The findings raise the possibility that oral health and chronic gum inflammation may influence neuroinflammatory disease progression.
Key facts
MS disability link: MS patients with high levels of F. nucleatum showed markedly higher disability scores. Oral-brain axis: The association was not observed in NMOSD or MOGAD, suggesting specific relevance to MS. Bridge of inflammation: Bacteria may act as a “bridge” between oral inflammation and neurological severity.
Source: Hiroshima University
There is increasing evidence to suggest that the serious gum disease periodontitis may contribute to central nervous system disorders through chronic inflammation. However, its role in multiple sclerosis, a chronic autoimmune disease of the central nervous system, is unclear.
A research team has conducted a study with findings that suggest a possible association between the relative abundance of Fusobacterium nucleatum (F. nucleatum), a bacteria found in the mouth, and disease severity in patients with multiple sclerosis (MS).
Their research is published in the journal Scientific Reports on November 3, 2025.
Multiple sclerosis is a central inflammatory demyelinating disease that attacks the myelin sheath, the protective layer that surrounds some nerve cells. While the specific cause of multiple sclerosis is unknown, viral infections, smoking, vitamin deficiencies, and genetic predispositions are thought to be possible contributing factors.
The prevalence of multiple sclerosis has steadily increased in Japan since the 1980s. This rapid increase could be influenced by environmental changes. Scientists have extensively studied the alterations in the gut microbiome related to this.
Recent attention has expanded to include the possible role of the oral microbiota, along with the gut microbiota, in diseases of the central nervous system.
Periodontal disease is a chronic bacterial infection that triggers persistent inflammation in the periodontal tissues. Ultimately, it destroys connective tissues and alveolar bone and causes tooth loss.
Periodontal disease is common, with a global prevalence of 40 to 60 percent. Researchers know it increases the risk of diseases such as atherosclerosis, diabetes and rheumatoid arthritis.
Exploring a possible ‘oral-brain axis’ in MS
In their study, the research team quantified periodontal bacterial load in tongue lining samples collected from patients with central inflammatory demyelinating diseases such as multiple sclerosis, neuromyelitis optica spectrum disorder (NMOSD), or myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD).
High relative abundance was determined based on whether the proportion of a given bacterial species in their oral samples was in the top 25% of all patients studied (high) or the bottom 75% (low).
They investigated the relationships between periodontal bacterial load and clinical factors and the differential effects of various bacterial species.
The team’s goal was to determine whether specific periodontal pathogens in the oral cavity are associated with the clinical severity of multiple sclerosis.
“While the gut microbiome has been extensively investigated in multiple sclerosis, the possible involvement of the oral microbiome remains largely unexplored.
“Because the oral cavity is an important source of chronic inflammation and represents a potentially modifiable factor, clarifying its relationship with the severity of multiple sclerosis is important for understanding the mechanisms of the disease and developing new preventive strategies,” said Masahiro Nakamori, associate professor and lecturer at Hiroshima University Hospital.
Their findings show that multiple sclerosis patients with a higher relative abundance of the periodontal pathogen Fusobacterium nucleatum in tongue lining samples showed significantly greater disability, as measured by the 10-point Expanded Disability Status Scale (EDSS).
“This association was not observed in neuromyelitis optica spectrum disorder or myelin oligodendrocyte glycoprotein antibody-associated disease, suggesting a potentially MS-specific ‘oral-brain axis’ through which oral inflammation may influence neuroinflammatory disease severity,” said Hiroyuki Naito, an assistant professor at Hiroshima University Hospital.
A ‘bridging bacteria’?
To rule out alternative explanations, the team tested a series of clinical factors along with the bacteria. Even after adjusting for age, disease duration, number of attacks, and multiple sclerosis subtype, high levels of Fusobacterium nucleatum were associated with tenfold increased odds of severe disability in patients with multiple sclerosis.
The team noted that nearly two-thirds (61.5%) of MS patients with a high relative abundance of Fusobacterium nucleatum were in the moderate to severe disability range (EDSS of 4 or greater), compared to about one-fifth (18.6%) of those with milder disease (EDSS less than 4).
No such association was observed in patients with neuromyelitis optica spectrum disorder or myelin oligodendrocyte glycoprotein antibody-associated disease. Multiple sclerosis patients with Fusobacterium nucleatum and at least one other periodontal pathogen showed even greater disability.
“Fusobacterium nucleatum may act as a hidden ‘bridging bacteria,’ not only linking bacterial communities in dental biofilms, but also potentially linking oral inflammation with neurological disability,” Nakamori said.
Looking ahead, the team hopes to conduct larger multicenter studies to validate the association between oral bacteria and the severity of multiple sclerosis. They plan to perform mechanistic analyses, including cytokine profiling and metagenomic sequencing, to understand how oral pathogens influence the immunopathology of multiple sclerosis.
It is also necessary to evaluate whether dental interventions, such as periodontal treatment or routine oral care, can modify disease activity or disability progression in multiple sclerosis.
“Ultimately, our goal is to clarify how the oral-gut-brain inflammatory axis contributes to the pathophysiology of multiple sclerosis and explore whether oral health could serve as a new target for disease modification,” Naito said.
The research team also includes Megumi Toko, Tomoko Muguruma, Hidetada Yamada, Takamichi Sugimoto, Yu Yamazaki, Kazuhide Ochi and Hirofumi Maruyama from the Department of Clinical and Therapeutic Neuroscience at Hiroshima University and Hiromi Nishi and Hiroyuki Kawaguchi from the Department of General Dentistry at Hiroshima University Hospital.
Key questions answered:
A: Yes. Elevated levels of Fusobacterium nucleatum were associated with significantly greater disability in patients with MS.
A: No. The association did not appear in neuromyelitis optica spectrum disorder or MOG antibody disease, suggesting a unique MS pathway.
A: Potentially. Researchers hope to study whether periodontal care can reduce inflammation and influence the progression of MS.
Editorial notes:
This article was edited by a Neuroscience News editor. Magazine article reviewed in its entirety. Additional context added by our staff.
About this multiple sclerosis research news
Author: Mikas Matsuzawa
Source: Hiroshima University
Contact: Mikas Matsuzawa – Hiroshima University
Image: Image is credited to Neuroscience News.
Original research: Open access.
“The periodontal pathogen Fusobacterium nucleatum is associated with disease severity in multiple sclerosis” by Masahiro Nakamori et al. Scientific Reports
Abstract
The periodontal pathogen Fusobacterium nucleatum is associated with disease severity in multiple sclerosis
Increasing evidence suggests that periodontitis may contribute to central nervous system disorders through chronic inflammation, but its role in multiple sclerosis (MS) remains unclear.
This cross-sectional exploratory study investigated the associations between the relative abundance of periodontal pathogens in the oral cavity and the clinical characteristics of MS.
We enrolled 98 patients with MS, neuromyelitis optica spectrum disorder, or myelin oligodendrocyte glycoprotein antibody-associated disease.
Tongue coating samples were analyzed by quantitative polymerase chain reaction targeting four periodontal species.
High relative abundance was defined as an abundance exceeding the third quartile in proportion to the total bacterial abundance. Associations between clinical and MRI characteristics were evaluated.
Among the 56 MS patients, only a high relative abundance of Fusobacterium nucleatum was associated with disease severity, as measured by the Expanded Disability Status Scale (EDSS) (p = 0.009).
No associations were observed for the other three pathogens or in the non-MS groups. In multivariate analysis, a high relative abundance of Fusobacterium nucleatum remained independently associated with EDSS score.
These findings suggest a possible association between the relative abundance of Fusobacterium nucleatum in the oral cavity and disease severity in MS.
