The purpose of this study is to learn the efficacy and safety of fecal microbiota transplantation (FMT) using stool from a donor with low proteolytic activity and containing the bacteria Alistipes putredinis in patients with irritable bowel syndrome (IBS) and high proteolytic activity. Proteolytic activity is the breakdown of proteins into smaller polypeptides or amino acids.

Inclusion Criteria:

• IBS defined by Rome IV criteria
• Non IBS-C
• Moderate to severe symptoms defined by IBS-SSS≥175
• Able to safely undergo and consent to colonoscopy

Exclusion Criteria

• Immune deficiency or treatment with immunosuppressive medications
• Severe bowel or medical disease precluding administration of bowel prep
• Severe bowel or medical disease precluding colonoscopy with conscious sedation
• Active cancer
• Pregnant or lactating
• Abdominal surgery (exception of splenectomy, partial hepatectomy, partial/unilateral nephrectomy, laparoscopy, pelvic floor repair, mesh, liposuction, fundoplication, tubal ligation, gastric sleeve, oophorectomy, hernia, appendectomy, cholecystectomy, caesarean section and hysterectomy)
• Severe psychiatric disorder (HADS-A or D>16), or diagnosed alcohol or drug abuse disorder
• New probiotics or treatment with antibiotics, NSAIDs (within 4 wks prior to study entry)
• Use of treatments known to affect colonic motility (with exception of loperamide)
• Diagnosed h/o bleeding disorder
• Organic GI diseases (IBD, celiac disease, microscopic colitis)
• Chronic kidney or liver disease
• Absolute neutrophil count (ANC) <500 IU/ml