Mycobacterium vaccae bacteria are already known to decrease anxiety, but it might have even more dramatic properties. Recent studies on mice suggest the bacteria, commonly found in the soils of people's gardens, also increases intelligence and the ability to learn.


Dorothy Matthews and Susan Jenks, both of The Sage Colleges in Troy, New York, sought to build on previous experiments in which dead strains of the bacteria were injected into mice, spurring the neurons of the mice to greatly increase serotonin production. The more immediate effect of all this extra serotonin, of course, was decreased anxiety levels, leading the earlier researchers to conclude M. vaccae has antidepressant qualities.

But Matthews was interested in a more indirect effect:

"Since serotonin plays a role in learning we wondered if live M. vaccae could improve learning in mice."


To assess this, Matthews and Jenks had two groups of mice; the experimental group was fed live specimens of the bacteria, while the control group was not. They were then tested in a maze to see how well the two groups could navigate the challenge.

The difference was striking:

"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."

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The mice were retested twice after the bacteria was removed from their diet. When they were tested almost immediately afterward, they weren't quite as proficient, but still got through the maze much faster than their control counterparts. Tested a final time three weeks later, the mice were still a little faster, but not to a statistically significant extent. This suggests the effect of the bacteria on learning is temporary, although humans with their greater cognitive capacity might be able to derive more lasting benefits from exposure to M. vaccae.

Certainly, Matthews thinks it's an idea that's worth following up on:

"This research suggests that M. vaccae may play a role in anxiety and learning in mammals. 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." [American Society of Microbiology]