As anyone who’s seen a yogurt commercial knows, our guts are teeming with bacteria. So, too, are our hands, feet, ears, and mouths.



But our brains?

Until recently, scientists would have said no way. The brain was long thought to be a kind of fortress, separated from the body by a virtually impenetrable barrier of specialized cells. Now, that view is beginning to shift, with increasing evidence that aliens can, and do, sneak in.

The latest evidence comes from a team of researchers in Canada, who found that a type of bacteria usually found in soil may make its way into some of our brains.

That possibility is “a mind-bending concept,” said Kathy Spindler, a professor of microbiology and immunology at the University of Michigan who was not involved in the new work. If confirmed, the study would “upset the dogma that the brain is normally a sterile site,” said Vincent Young, an infectious diseases physician and microbiologist also at the University of Michigan. If living bacteria help to maintain brain health in some way, disruptions to them, for example from antibiotics, could contribute to disease. (In other parts of the body, disruptions to native bacteria may play a role in some asthma, food allergies, inflammatory bowel disease, and even obesity, he added.)....