Companion diagnostic method for use in the treatment of irritable bowel syndrome with dietary interventions or faecal microbiota transplant

An in vitro method to determine the likelihood that a subject with irritable bowel syndrome (IBS) will respond to treatment with a low Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols (FODMAP) diet, said method comprising

• (i) determining for a test sample from the gastrointestinal (GI) tract of a subject with constipation subtype IBS to be treated with a low FODMAP diet the amount of bacteria from at least one taxonomic group selected from
• Clostridium methylpentosum,
• Eubacterium siraeum,
• Acinetobacter junii, and
• Desulfitispora alkaliphila;
• and
• (ii)(a) comparing the amount of said bacteria from said at least one taxonomic group with a reference value prepared from at least one sample from the GI tract of at least one subject non-symptomatic for IBS, and determining if the amount of said bacteria from said at least one taxonomic group in said test sample differs from, or corresponds to, the reference value, wherein an amount of bacteria in the taxonomic groups Clostridium methylpentosum or Eubacterium siraeum which is greater than the reference values, or an amount of bacteria in the taxonomic groups Acinetobacter junii or Desulfitispora alkaliphila which is lower than the reference values is indicative that the subject will respond to a low FODMAP diet;
• and/or
• (ii)(b) comparing the amount of said bacteria from said at least one taxonomic group with a cut-off value which has been determined as a median amount of said bacteria in at least one sample from the GI tract of at least one IBS subject with said IBS subtype which has been previously shown to be responsive to said treatment and determining if the amount of said bacteria from said at least one taxonomic group in said test sample is greater than or less than said median cut-off value, wherein an amount of bacteria in the taxonomic groups Clostridium methylpentosum or Eubacterium siraeum which is greater than said median cut-off value for said bacteria, or an amount of bacteria in the taxonomic groups Acinetobacter junii or Desulfitispora alkaliphila which ich is less than said median cut-off value for said bacteria is indicative the bis WI respond to a low FODMAP diet.