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