The enigmatic 'brain microbiome' could play a role in neurological disease

The microbes that live in your gut are having their moment in the sun. Even if you haven't been following the research, you can't have missed the hundreds of adverts for probiotics and prebiotics, aimed at selling you products to keep your microbiome healthy.

Other microbiomes have also recently been discovered, and these too play an important role in your Health. Your mouth, nasal cavity, skin and scalp all have their own unique microbiomes. Some have even proposed that the brain has its own microbiome.

The idea that the brain has a microbiome was first suggested in 2013, but it didn't get much attention. This is mostly due to the longstanding belief that the brain is a sterile organ, shielded from the rest of the body and from harmful agents that are circulating in our blood.

It is also difficult to confirm the presence of microbes. The techniques used rely on analyzing foreign genetic material, which can be unreliable because these fragments of DNA could be the result of contamination.

In healthy brains, the so-called "blood-brain barrier" shields the brain from the blood and any harmful substances dissolved in it. However, during aging and in neurological diseases such as Alzheimer's disease, this protective barrier becomes leaky and blood and harmful substances can enter the brain.

This can cause diseases and further worsen the damage that has already occurred. Similarly, the immune system also becomes less effective as we age. This could also contribute to the presence of microorganisms throughout the body that might have been cleared away by immune cells in younger people.

The previously mentioned 2013 study investigated whether microbes can invade the brains of people with HIV/AIDS. They compared brain tissue of people with HIV/AIDS to brain tissue of people without HIV/AIDS. Surprisingly, they found non-human genetic material that pointed to the presence of more than 173 types of bacteria and phages (viruses that infect bacteria) in the brains they studied.