Looking at previously published studies in the field, O’Sullivan and colleagues say a stool from a super-donor often has a greater diversity of microbes. However, they add for some conditions, including inflammatory bowel disease, specific components are important such as whether the stool is richer in particular bacteria – such as those which produce certain chemicals.In other studies, it has been suggested the presence of viruses in the stool might play a role in resolving certain conditions. “We think the super-donors differ depending on the condition you are trying to treat,” said O’Sullivan.

The team added that compatibility between the donor and recipient is another key factor, not least the immune reaction of the recipient to the donor stool, and which species and strains are present in the recipient’s gut before transplant.