A new study among multiple sclerosis patients suggests those with a high relative abundance of Fusobacterium nucleatum, in combination with other periodontal bacteria, were more likely to have moderate to severe disability than those without this bacterial combination. No similar link was seen in neuromyelitis optica spectrum disorder or myelin oligodendrocyte glycoprotein antibody-associated disease, suggesting the co-occurrence of oral pathogens may be particularly relevant to disability severity in MS.

Increasing evidence suggests periodontitis, the severe gum disease, may contribute to central nervous system disorders through chronic inflammation. However, its role in MS has been unclear. A study conducted by a Hiroshima University Hospital research team suggests a potential link between the relative abundance of Fusobacterium nucleatum, a bacterium found in the mouth, and disease severity in MS patients.

MS is a central inflammatory demyelinating disease that targets the myelin sheath, the protective layer that wraps around some nerve cells. While the specific cause of MS remains unknown, viral infections, smoking, vitamin deficiencies, and genetic predispositions are thought to be possible contributing factors.

The prevalence of MS has been increasing in Japan since the 1980s. This increase might be influenced by environmental changes. Scientists have studied alterations in the gut microbiome related to this. Recent attention has expanded to include the possible role of oral microbiota, alongside gut microbiota, in central nervous system diseases.

Periodontal disease is a chronic bacterial infection that triggers persistent inflammation in periodontal tissues. It ultimately destroys the connective tissues and alveolar bone, resulting in 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.

In their study, the research team quantified the periodontal bacterial load in tongue coating samples collected from patients with central inflammatory demyelinating diseases such as MS, neuromyelitis optica spectrum disorder, or myelin oligodendrocyte glycoprotein antibody-linked disease. High relative abundance was determined based on whether the proportion of a given bacterial species in their oral samples was in the top 25 percent of all patients studied (high) or in the bottom 75 percent (low).

They examined the relationships between the periodontal bacterial load and clinical factors and the differential effects of various bacterial species. They aimed to determine whether specific periodontal pathogens in the oral cavity are linked to clinical severity in MS. Findings show MS patients with a higher relative abundance of the periodontal pathogen Fusobacterium nucleatum in tongue-coating samples showed significantly greater disability, as measured by the 10-point Expanded Disability Status Scale.

To rule out alternative explanations, the team tested a range of clinical factors alongside the bacterium. Even after adjusting for age, disease duration, number of attacks, and MS subtype, high levels of Fusobacterium nucleatum were linked to about tenfold higher odds of severe disability in MS patients.

The team noted that nearly two-thirds of MS patients with a high relative abundance of Fusobacterium nucleatum fell into the moderate-to-severe disability range (EDSS of 4 or greater), compared with roughly one-fifth of those with milder disease (EDSS below 4). No such association was observed in patients with neuromyelitis optica spectrum disorder or myelin oligodendrocyte glycoprotein antibody-associated disease. MS patients with both Fusobacterium nucleatum and at least one other periodontal pathogen showed even higher disability.

The team hopes to conduct larger, multicenter studies to validate the link between oral bacteria and MS severity. They plan to perform mechanistic analyses, including cytokine profiling and metagenomic sequencing, to understand how oral pathogens influence MS immunopathology. There is also a need to evaluate whether dental interventions — such as periodontal treatment or routine oral care — may modify disease activity or disability progression in MS.

The study was published in the journal Scientific Reports.