Fig. 1.

Relationship between dysbiosis in the gut microbiota and disease. (A) A bidirectional communication is present between the brain and gut. The gut passes a signal to the brain via the intrinsic primary afferent nerve and the vagus nerve. The brain also regulates the gut through neurologic, immunologic, and hormone messages in various physiopathological conditions. (B) Dysbiosis in the gut microbiota affects several neurological and gut-related diseases. ASD, autism spectrum disorder; AD, Alzheimer’s disease; PD, Parkinson’s disease; IBD, inflammatory bowel disease; IBS, irritable bowel syndrome; CDI, Clostridium difficile infection.