The Safety and Efficacy of Fecal Microbiota Transplantation in a Population With Major Depressive Disorder

Inclusion Criteria:

1. Between 18-65 years of age: Participants should be at least 18 years old and not older than 65 years at the day ofscreening
2. Have a primary diagnosis of MDD according to the M.I.N.I. InternationalNeuropsychiatric Interview (MINI)47
3. Medical history suggestive of Treatment Resistant Depression (TRD). (inadequateresponse to at least 2 approved antidepressants. at least one of which is in thecurrent episode of depression)48
4. Have been on a current treatment with a approved antidepressant at an adequate dosefor at least 8 weeks
5. A MADRS score of ≥ 19 at screening and visit 2 Additional Inclusion Criteria:

• Participants who will be included in the IBS-D cohort should have a confirmed diagnosisof IBS-D as indicated by the referring gastroenterologist.

Exclusion Criteria:

• 1. Participant meets Diagnostic and Statistical Manual of Mental Disorders (DSM-5)1Criteria for the following conditions according to the M.I.N.I: f) Substance UseDisorder within the last 3 months. *(Criteria should include Alcohol and non-alcoholsubstances except Cannabis) g) Moderate or severe Substance use disorder for Cannabisuse the last 3 months h) Active Anorexia Nervosa or Bulimia nervosa i) Schizophreniaor schizoaffective disorder j) Active suicidality 2. Regular intake of non-steroidalanti-inflammatory drugs, antibiotics, or iron supplements for medical purposes in the 3 months prior to study entry 3. Use of prebiotics or probiotics for medical purposesfor more than 2 weeks within the last 3 months 4. Clinically diagnosed chronicgastrointestinal diseases (IBD, Crohn's disease, Ulcerative colitis, Celiac disease)

5. Conditions causing immune suppression 6. Not breastfeeding, pregnant or seeking toget pregnant during the course of this study. Be using an acceptable method of birthcontrol (implants, injectable, combined oral contraceptives, IUDs, sexual abstinenceor a vasectomized partner) 7. Reported allergy to Vancomycin or Nitazoxanide