Research on the microbiota–gut–brain axis has moved from demonstrating that gut microorganisms can influence brain chemistry and behavior to identifying the mechanisms that may carry microbial signals from the intestine to the central nervous system. 

In this interview, Stephen Michael Collins, Professor at McMaster University and a pioneer in the field, retraces some of the key experimental evidence linking the gut microbiota with behavioral changes, anxiety, depression and irritable bowel syndrome, before focusing on an emerging mechanism of communication: bacterial outer membrane vesicles. Produced particularly by Gram-negative bacteria, these nanoscale structures can protect and transport proteins, DNA fragments and other bacterial molecules across biological barriers, potentially reaching the brain and modulating neuroinflammation and neuronal function. Their effects may differ substantially according to the microorganism of origin, ranging from pro-inflammatory signaling to potentially beneficial modulation of neuroinflammation. According to Collins, these vesicles may therefore represent not only a new component of the microbiota–gut–brain axis, but also a promising platform for future targeted drug, vaccine and immunotherapy delivery.