Exposure to specific bacteria in the environment, already believed to have antidepressant qualities, could increase learning behavior according to research presented today at the 110th General Meeting of the American Society for Microbiology in San Diego.
“Mycobacterium vaccae is a natural soil bacterium which people likely ingest or breath in when they spend time in nature,” says Dorothy Matthews of The Sage Colleges in Troy, New York, who conducted the research with her colleague Susan Jenks.
Previous research studies on M. vaccae showed that heat-killed bacteria injected into mice stimulated growth of some neurons in the brain that resulted in increased levels of serotonin and decreased anxiety.
“Since serotonin plays a role in learning we wondered if live M. vaccae could improve learning in mice,” says Matthews.
Matthews and Jenks fed live bacteria to mice and assessed their ability to navigate a maze compared to control mice that were not fed the bacteria.
“We found that mice that were fed live M. vaccae navigated the maze twice as fast and with less demonstrated anxiety behaviors as control mice,” says Matthews.
In a second experiment the bacteria were removed from the diet of the experimental mice and they were retested. While the mice ran the maze slower than they did when they were ingesting the bacteria, on average they were still faster than the controls.
A final test was given to the mice after three weeks’ rest. While the experimental mice continued to navigate the maze faster than the controls, the results were no longer statistically significant, suggesting the effect is temporary.
“This research suggests that M. vaccae may play a role in anxiety and learning in mammals,” says Matthews. “It is interesting to speculate that creating learning environments in schools that include time in the outdoors where M. vaccae is present may decrease anxiety and improve the ability to learn new tasks.”
The results so far suggest that simply inhaling M. vaccae—you get a dose just by taking a walk in the wild or rooting around in the garden—could help elicit a jolly state of mind. “You can also ingest mycobacteria either through water sources or through eating plants—lettuce that you pick from the garden, or carrots,” Lowry says.
Graham Rook, an immunologist at University College London and a coauthor of the paper, adds that depression itself may be in part an inflammatory disorder. By triggering the production of immune cells that curb the inflammatory reaction typical of allergies, M. vaccae may ease that inflammation and hence depression. Therapy with M. vaccae—or with drugs based on the bacterium’s molecular components—might someday be used to treat depression. “It’s not clear to me whether the way ahead will be drugs that circumvent the use of these bugs,” Rook says, “or whether it will be easier to say, ‘The hell with it, let’s use the bugs.’”