Unexpected Evidence of a Brain Microbiome

The outdated notion that bacteria are harmful invaders in the body was challenged further when researchers found bacteria in the brain

Researchers have discovered that bacteria reside in our brain, raising profound questions about our connection to the microscopic natural world. Lia Koltyrina/Shutterstock

By now, almost everyone has heard of the human microbiome—the collection of viruses, bacteria, and fungi that play a pivotal role in our health and cognitive functioning. Also called the microbiota, we’ve long assumed that the microbiome consists of microbes that reside along our gastrointestinal tract—and more recently, on our skin.

That’s logical enough; microbes live on our interfaces with the outside world. Conversely, there are certain areas in the human body that are assumed to be sterile, aka free of microbes, like the eye and the womb. However, advances in analytical techniques enabled researchers to recently identify the placental microbiome and eye microbiome that are present in healthy people. That’s pretty cool, but there definitely couldn’t be microbes in our brains, the most protected area of our bodies, right?

A head-turning poster at the November 2018 Society for Neuroscience scientific conference called into question the assumption of the brain as a sterile, bacteria-free zone. A team of researchers from The University of Alabama–Birmingham (UAB), led by Professor Rosalinda Roberts, showed high-resolution microscope images of mouse and human brains that depicted bacteria happily residing in astrocytes, star-shaped brain cells that interact with and support neurons.

A Scanning Electron Microscope image of a human brain slice showing bacteria (circled in red) next to a blood vessel. Adapted from a writeup in Science Magazine.