There has been a re-emergence of interest in the interplay between the faecal microbiota and its associated metabolisms and gastrointestinal function. This has recently been driven by the current interest in human and veterinary probiotics, and in the recent past by hypotheses which linked gut bacterial metabolism of ingested foodstuffs and colorectal and other cancers. However, what is less widely known is the extent of involvement of gastrointestinal bacteria in gut function, gut disease, and particularly diseases of other organs.

Some of the less generally well known aspects of this interplay relate to gut bacterial metabolites: for example, the production of volatile fatty acids exacerbating acidaemias such as methylmalonic acidaemia, and the associated role of antibiotics in patient management.1 An area where there has been a resurgence of interest is the production of …