Gut microbiome interaction goes beyond commensal function as vitamin production or support nutrients digestion. It also interplays with the host immune system and may be related to the development of immune-mediated diseases. Multiple sclerosis patients have dysbiosis compared to healthy individuals. But how this relates to disease development and severity is still uncertain. Dietary change including probiotic mixtures or ketogenic regimen has proven to change microbiome in multiple sclerosis (MS) subjects to one similar to healthy controls. However, proof of clinical benefits is lacking. We dissert on current knowledge about immune system and gut bacteria interactions. We discuss faecal microbial transplantation as a potential intervention to ameliorate gut dysbiosis in MS as well as the caveats of a clinical trial design.