We read with interest the commentary of Raes1 on the growing clinical role of microbiome-based companion diagnostics. We agree that the future of microbiome in medical practice will be in using markers for diagnosis as well as predicting and personalising treatment. We report here new observations on a colonic bacteria that, while traditionally considered a commensal, may be important in chronic diarrhoea and IBS. Colonisation of the colon by Brachyspira aalborgi and B.
