Summary: Higher levels of the periodontal bacterium Fusobacterium nucleatum in the oral cavity are associated with greater disability in people with multiple sclerosis (MS). Researchers analyzed tongue coating samples and found that MS patients with the highest relative abundance of this bacterium had significantly worse scores on the Expanded Disability Status Scale (EDSS).
This effect appeared specific to MS and was not observed in two other central inflammatory demyelinating diseases—neuromyelitis optica spectrum disorder (NMOSD) or myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD)—supporting the idea of an MS-specific oral–brain inflammatory link. The findings highlight how oral health and chronic gum inflammation might influence neuroinflammatory disease progression.
Key Facts
- MS Disability Link: MS patients with elevated Fusobacterium nucleatum showed substantially higher disability scores on EDSS.
- Oral–Brain Axis: The association was not detected in NMOSD or MOGAD, suggesting a disease-specific relationship in MS.
- Inflammation Bridge: Fusobacterium nucleatum may serve as a “bridge” linking oral inflammation to increased neurological severity.
Source: Hiroshima University
Growing evidence indicates that periodontitis—chronic gum disease—can contribute to central nervous system disorders through sustained inflammation. Its influence on multiple sclerosis, a chronic autoimmune condition of the central nervous system, has been uncertain. A research team led by investigators at Hiroshima University examined whether the oral abundance of periodontal pathogens relates to clinical severity in MS.
The study, published in Scientific Reports on November 3, 2025, focused on how periodontal bacteria in the mouth might associate with clinical measures of disease activity and disability in central inflammatory demyelinating disorders.
Multiple sclerosis damages the myelin sheath that insulates nerve fibers. While the exact cause of MS remains unknown, a combination of environmental factors, infections, lifestyle elements, nutritional status, and genetics are thought to contribute. Incidence and prevalence of MS have been rising in Japan since the 1980s, prompting investigation into environmental and microbiome influences.
Researchers have previously studied the gut microbiome in MS; this study expands the scope to the oral microbiome. The oral cavity is a major reservoir of chronic inflammation and an easily modifiable target, making it a relevant focus for understanding disease mechanisms and for potentially preventing progression.
Exploring a potential ‘oral–brain axis’ in MS
In a cross-sectional analysis, the researchers collected tongue-coating samples from 98 patients with central inflammatory demyelinating diseases—56 with MS and the remainder with NMOSD or MOGAD. They used quantitative polymerase chain reaction (qPCR) to measure four periodontal species and defined “high relative abundance” as being above the third quartile for each species.
After comparing bacterial abundance with clinical data, MRI features, and established measures such as the EDSS, the team found that only Fusobacterium nucleatum showed a significant relationship with disease severity among MS patients. High levels of this bacterium corresponded to worse disability scores (p = 0.009).
This relationship remained significant after adjusting for potential confounders including age, disease duration, number of relapses, and MS subtype. In multivariate analysis, a high relative abundance of Fusobacterium nucleatum was independently associated with approximately tenfold greater odds of moderate-to-severe disability in MS patients.
The pattern was specific to MS: NMOSD and MOGAD patients did not show the same association. MS patients who carried Fusobacterium nucleatum alongside at least one other periodontal pathogen displayed even greater disability, suggesting a possible additive effect of mixed oral pathogens.
A ‘bridge bacterium’?
Investigators propose that Fusobacterium nucleatum could function as a hidden “bridge bacterium,” connecting bacterial communities in dental biofilms and potentially linking persistent oral inflammation to neurological damage. While causation cannot be established from this cross-sectional study, the results support further evaluation of the oral microbiome as a contributor to MS immunopathology.
The research team plans larger, multi-center studies and mechanistic work—such as cytokine profiling and metagenomic sequencing—to clarify how oral pathogens might influence immune responses in MS. They also emphasize the need to test whether periodontal treatment or routine oral care interventions can alter disease activity or slow disability progression.
“Ultimately, we aim to map how the oral–gut–brain inflammatory axis contributes to MS pathophysiology and to determine whether improving oral health could become a novel approach to disease modification,” said Hiroyuki Naito, assistant professor at Hiroshima University Hospital.
The study team includes Masahiro Nakamori, Megumi Toko, Tomoko Muguruma, Hidetada Yamada, Takamichi Sugimoto, Yu Yamazaki, Kazuhide Ochi, Hirofumi Maruyama, Hiromi Nishi, and Hiroyuki Kawaguchi from Hiroshima University.
Key Questions Answered:
A: Yes. In this study, a high relative abundance of Fusobacterium nucleatum in tongue-coating samples was associated with significantly greater disability in MS patients.
A: No. The association was not found in NMOSD or MOGAD, suggesting the relationship may be specific to MS.
A: Potentially. The authors recommend trials to determine whether periodontal care or improved oral hygiene can reduce inflammation and influence MS progression.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional context was added by editorial staff.
About this multiple sclerosis research news
Author: Mikas Matsuzawa
Source: Hiroshima University
Contact: Mikas Matsuzawa – Hiroshima University
Image: The 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
Periodontitis has been implicated in central nervous system disorders via chronic inflammation, but its role in multiple sclerosis remains unclear. This exploratory, cross-sectional study assessed whether the oral relative abundance of periodontal pathogens relates to clinical characteristics in MS.
Ninety-eight patients with MS, NMOSD, or MOGAD were enrolled. Tongue-coating samples were analyzed by qPCR for four periodontal species. High relative abundance was defined as values above the third quartile. Clinical and MRI associations were evaluated.
Among 56 MS patients, only a high relative abundance of Fusobacterium nucleatum correlated with greater disease severity measured by EDSS (p = 0.009). No significant associations were found for the other pathogens or in the non-MS groups. Multivariate analysis confirmed that high Fusobacterium nucleatum abundance remained independently associated with EDSS score.
These results point to a potential link between oral Fusobacterium nucleatum levels and MS severity, supporting further research into oral–brain inflammatory pathways and the potential for oral-health-based interventions in MS care.