Clinical depression may be treatable with bacteria, doctors at Bristol University posit. They got the idea when they observed lung cancer patients inoculated with harmless Mycobacterium vaccae who showed reduced symptoms and improved mental health. The brain produces serotonin as an immune response, the docs hypothesized, raising the low serotonin levels associated with depression and resulting in a sunnier outlook.
Successful testing in mice—whose stress levels can apparently be measured by watching how they swim when dropped into a tiny pool—suggests that M. vaccae may work as a vaccination for depression. Test results have also stimulated new theories about the immune system being responsible for the rise in clinical depression.