Could gut bacteria influence multiple sclerosis?

Scientists have long suspected that the gut bacteria might play a role in diseases like multiple sclerosis (MS). However, determining whether MS alters the gut microbiota or if microbiota changes contribute to MS remains a challenge. A new study published in PNAS Immunology and Inflammation1 has identified bacterial biomarkers linked to MS severity, paving the way for better disease management and reinforcing the importance of the gut-brain axis.

 

What is multiple sclerosis?

Multiple sclerosis is a chronic autoimmune disease that affects the brain and spinal cord. Normally, if you e.g. get a cut while gardening, the immune system is being activated to fight off harmful bacteria or remove foreign objects like splinters. However, in autoimmune diseases like type 1 diabetes or lupus, the immune system goes into overdrive and mistakenly attacks healthy cells. In MS, it targets the protective layer around nerves, leading to symptoms such as fatigue, difficulty walking, numbness, vision problems, and cognitive decline. While there is no cure for MS, treatments focus on managing symptoms, slowing disease progression, and modulating the immune system.

The exact cause of multiple sclerosis remains unknown, but several factors have been implicated, including genetic predisposition, environmental triggers like vitamin D deficiency and viral infections, and lifestyle factors such as smoking and obesity. Women are more likely to develop MS than men, and individuals with other autoimmune diseases, such as psoriasis, may also have a higher risk2. Additionally, imbalances in gut microbiota have been suggested as a contributing factor3.

 

Gut microbiota and multiple sclerosis: the study and key findings

A research team led by Dr. Ashutosh K. Mangalam at the University of Iowa analyzed stool samples from 51 healthy individuals and 45 MS patients to identify key bacterial markers associated with the disease. They then transplanted bacteria isolated from these stool samples into mice engineered to mimic MS symptoms. This allowed them to investigate potential causal relationships between specific bacteria and MS progression. Expanding their research, they tested their gut biomarker in a larger cohort of 572 MS patients and their household controls, providing robust evidence for a microbial signature associated with the disease.

 

The study uncovered several important insights:

  • People with MS showed distinct differences in gut bacteria compared to healthy individuals.
  • A specific microbial imbalance, lower Bifidobacterium and higher Akkermansia, was linked to disease severity.
  • Transferring MS-related bacteria to mice caused inflammation and symptoms resembling MS, suggesting a possible causal role.

First, researchers confirmed that MS patients had signs of more inflammation in their gut and blood compared to healthy individuals. When the researchers compared the gut microbiota of MS patients to healthy individuals, they found that while the overall bacterial diversity was similar, specific types of bacteria differed. These differences were consistent regardless of treatment status, body mass index, sex, or age, suggesting that MS is the major gut microbiome modulator in that context.

One of the key patterns involved a shift in the balance between two bacterial groups: Bifidobacterium and Akkermansia. In mice with MS-like symptoms, Akkermansia species were more abundant, while Bifidobacterium were reduced. As the disease progressed, this imbalance became more pronounced—when Akkermansia increased, Bifidobacterium decreased.

To explore whether this microbial shift could play a role in MS, the researchers introduced Blautia bacteria—identified as an important driver of MS —into antibiotics treated healthy mice. These mice were then given a healthy human microbiome by fecal microbiota transfer. Blautia bacteria triggered changes in gut microbiota that closely resembled those seen in human MS patients, along with increased levels of inflammation and more severe symptoms.

Among the most promising findings was the identification of a potential new stool biomarker: the ratio between Bifidobacterium adolescentis and Akkermansia muciniphila. In MS patients, this ratio was significantly lower. Because A. muciniphila is known for degrading the gut’s protective mucus layer, this could increase gut permeability and contribute to immune activation. However, further studies are needed to confirm this mechanism.

 

Why does this matter?

This study highlights the strong link between gut bacteria and multiple sclerosis, suggesting that tracking specific bacteria could help predict disease severity. In the future, adjusting gut bacteria through diet or other therapies might become a way to manage MS symptoms.

 

References:

  1. Ghimire, P.C. Lehman, L.S. Aguilar Meza, S.K. Shahi,J. Hoang,H. Olalde,M. Paullus, C. Cherwin, K. Wang, C. Gill, T. Cho, & A.K. Mangalam, Specific microbial ratio in the gut microbiome is associated with multiple sclerosis, Proc. Natl. Acad. Sci. U.S.A. 122 (10) e2413953122 (2025).
  2. Mayo Clinic. (n.d.). Multiple sclerosis – Symptoms and causes. Retrieved April 3, 2025, from https://www.mayoclinic.org/diseases-conditions/multiple-sclerosis/symptoms-causes/syc-20350269
  3. Correale, J., Hohlfeld, R. & Baranzini, S.E. The role of the gut microbiota in multiple sclerosis. Nat Rev Neurol18, 544–558 (2022).