Can depression be transferred via microbes? 

The gut-brain axis–the fascinating connection between gut microbes and the brain–sounds like science fiction. How can such tiny creatures affect our mood and behavior? How much of this story is hype and how much is real, useful science?

In 2003, Nobuyuki Sudo and colleagues noticed that germ-free mice behaved differently than normal mice.[1] They had a heightened reaction to stress and preferred to play alone. Since mice are generally sociable, this was a notable difference, and it all came down to their lack of microbes: when Sudo gave them a blend of non-pathogenic microbes, their behavior recovered. A healthy microbiota seemed to confer resilience to stress and made the mice more gregarious. The results raised eyebrows in all the fields affected: gastroenterology, neurology, psychiatry, immunology, endocrinology and microbiology. How could brainless microbes possibly affect the sophisticated mind of an animal?

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