Rarely, a fecal microbiota transplant worsens IBD, which suggests that gut microbes could play a role in the development or progression of the disease.[1] Though the gut microbiomes of people with IBD tend to differ from those of healthy individuals, a consistent, disease-specific pattern hasn’t been identified.[2]
One study found that several groups of bacteria — most of which are salivary — were elevated uniquely in IBD compared to other diseases. However, this doesn’t suggest that they play any role in IBD. It could simply have been a reflection of their higher relative abundance compared to abnormally low levels of other bacteria.[2]