Mycobacterium vaccae: The Bacteria That Makes You Happier and Smarter?

You have probably never heard of this microbe, but you might have inhaled or ingested a few while working in the garden. The bacterium, Mycobacterium vaccae, is thought to act as an antidepressant by stimulating the production of serotonin and norepinephrine in the brain.

Researcher Dorothy Matthews at The Sage Colleges in Troy, New York, and her colleague Susan Jenks conducted an experiment on mice whereby some of the mice were fed the live M. vaccae bacteria, and the others (the control group) were not. It was observed that the mice who had ingested this bacteria were able to find their way through a maze quicker than the other mice, while also demonstrating less anxiety than the control group.

After three weeks, the mice that had been injected with M. vaccae were still faster at the maze than the other mice. However, there was not a huge statistical difference, which shows the effect is temporary.

Another researcher, neuroscientist Christopher Lowry of the University of Bristol in England, wanted to know how M. vaccae might act on the brain to influence mood. He anesthetized six mice and injected powdered (dead and pulverized) M. vaccae bacteria directly into the trachea of each. The mice were then killed and Lowry found there had been an increased production level of serotonin-inducing proteins called cytokines (cell-signaling molecules) in the bodies.

Lowry's research team also dissected the brains of the mice to see if there were any neurons in the brain that might have been activated by the bacteria. They found more serotonin had been produced in the prefrontal cortex of the M. vaccae treated mice and that neurons in a region of the brain called the dorsal raphe nucleus were more active in the bacteria-treated mice than in the others. The part of the raphe that was activated has neurons that connect with other parts of the brain, which regulate mood and cognitive function, such as the hippocampus and prefrontal cortex.

The final test Lowry and his research team conducted was a stress-response test on a different set of mice. In this test, the mice are dropped in water for five minutes to see how long they will swim before they switch to floating. It is known that antidepressants increase swimming behavior in mice, and it was found that M. vaccae had the same effect on the mice as an antidepressant. Those treated with the bacteria swam for four minutes while the control mice only swam, on average, for two and a half minutes before giving up.

I wonder if we will start to see capsules of pure, live M. vaccae become a new probiotic supplement on health food shelves in the future, or hear of psychiatrists recommending them for their depressed and anxious patients. In the meantime, I guess we will just have to take up gardening and walking through the woods to boost our mood.

RESOURCES AND FOR FURTHER READING:

Ingestion of Mycobacterium vaccae decreases anxiety-related behavior and improves learning in mice (abstract of the study)

Is Dirt the New Prozac? (Discover Magazine)

Dirt Can Make You Happy (Horticulture Magazine)

Can Bacteria Make You Smarter? (Science Daily)

Soil Bacteria Might Increase Learning (Scientific American)

How to Get High on Soil (The Atlantic) 

Dorothy Matthews' Ph.D (The Sage College's Faculty Page)