Vancomycin Study in Multiple Sclerosis (MS)

Inclusion Criteria: * aged 18 - 50 * newly diagnosed MS (2017 McDonald criteria), CIS or RIS patients, who have experienced symptoms no earlier than the past year * treatment naive * able to understand the risks, benefits, and alternatives of participation and give meaningful consent Exclusion Criteria: * antibiotic use within the past 90 days; * pre- or probiotic use within past month or corticosteroids use within the past month; * use of tobacco products within the past 1 month; * history of treatment with immunosuppressants; * history of gastroenteritis within the past month or diagnosis with a chronic infectious disease, i.e. hepatitis B, C or HIV; * pregnancy or less than 6 months postpartum; * irritable bowel syndrome and other bowel dysfunction such as constipation; * history of bowel surgery; * inflammatory bowel disease, rheumatoid arthritis, systemic lupus erythematosus, diabetes and any other auto-immune illness; * diagnosis with another neurological disease, behavioral or psychiatric conditions that would be incompatible with a safe and successful participation in the study (such as severe major depression, schizophrenia and presence of psychotic symptoms); * eating disorders such as anorexia nervosa, bulimia, or binge eating syndrome; * travel outside of the country within the past month; * contraindication to vancomycin including estimated glomerular filtration rate of \<60ml/min, impaired hearing or known allergy. * Contraindication to MRI such as implanted metallic objects