Inclusion Criteria:  Between 18-60 years of age:  Participants should be at least 18 years old and not older than 60 years at the day of screening  Have a primary diagnosis of MDD as assessed/confirmed by the M.I.N.I. International Neuropsychiatric Interview (MINI) Have had a well-documented inadequate response to at least 2 approved antidepressants A MADRS score of ≥ 19 at screening and visit 2a Have a comorbid diagnosis of IBS. IBS patients can include any of the following: diarrhea predominant IBS (IBS-D), constipation predominant IBS (IBS-C), IBS with mixed bowel habits (IBS-M), or unclassified with IBS (IBS-U) as confirmed by the referring doctor using ROME III criteria Moderate-to-severe IBS symptoms, as indicated by a score of ≥175 on the IBS Severity Scoring System (IBS-SSS)  Exclusion Criteria:  Participant meets Diagnostic and Statistical Manual of Mental Disorders (DSM-5)[1] Criteria for the following conditions according to the M.I.N.I:  Substance Use Disorder within the last 3 months. *(Criteria should include Alcohol and non-alcohol substances except Cannabis) Moderate or severe substance use disorder for Cannabis use the last 3 months Active Anorexia Nervosa or Bulimia nervosa Schizophrenia, schizoaffective or bipolar disorder Active suicidality Regular intake of non-steroidal anti-inflammatory drugs, antibiotics, or iron supplements for medical purposes in the three (3) months prior to study entry Use of prebiotics or probiotics for medical purposes for more than two (2) weeks within the last three (3) months Conditions causing immunosuppression Women who are breastfeeding, pregnant or seeking to get pregnant during the course of this study. Not using an acceptable method of birth control (implants, injectable, combined oral contraceptives, IUDs, sexual abstinence or a vasectomized partner)