Scientists have identified specific gut bacteria that appear to trigger multiple sclerosis (MS). In a groundbreaking study conducted at Ludwig Maximilian University of Munich, researchers examined 81 pairs of identical twins in which only one sibling had MS. This unique design allowed them to control for genetic and environmental factors, isolating the role of the microbiome. The team found that two bacterial species, Eisenbergiella tayi and Lachnoclostridium, were significantly more abundant in the twins with MS. When these microbes were transferred into mouse models, they directly induced MS-like autoimmune symptoms, providing strong causal evidence. This is the most precise identification of microbial triggers for MS to date and adds powerful support to the gut-brain axis in autoimmune disease. The discovery raises hope for new approaches to early detection, prevention, and treatment — potentially by targeting or modulating these specific bacteria before symptoms appear. While human clinical trials are still needed, the findings represent a major step toward microbiome-based therapies for MS and other autoimmune conditions. [Yoon, H., Gerdes, L. A., Beigel, F., Sun, Y., Kövilein, J., Wang, J., Kuhlmann, T., Flierl-Hecht, A., Haller, D., Hohlfeld, R., Baranzini, S. E., Wekerle, H., & Peters, A. (2025). Multiple sclerosis and gut microbiota: Lachnospiraceae from the ileum of MS twins trigger MS-like disease in germfree transgenic mice—An unbiased functional study. Proceedings of the National Academy of Sciences, 122(18), e2419689122. DOI: 10.1073/pnas.2419689122]