Does Bacteria Live in Human Brains?

Brain has defense system called ‘blood-brain barrier’ which prevents germs and toxins entering the brain from the blood circulation. It allows only necessary things like water, amino acids, glucose and lipids to enter the brain. We know that bacteria live in the gastrointestinal tract (gut) of humans and animals. We generally thought that, in normal condition, brain is free of microbial colonies. But, certain bacteria and viruses can infect the brain and cause fatal diseases. Previously in 2013, one study showed RNA evidence of presence of bacteria in the human brains from patients with HIV infection and other diseases. Currently, a pilot study has revealed the presence of bacteria in the human brains of both normal and schizophrenia people. 

(Does Bacteria Live in Brain? Photo Courtesy: Geralt, Pixabay)

Scientists from the University of Alabama, Birmingham, USA have presented their discovery at a prestigious annual Neuroscience conference, organized by the Society for Neuroscience, USA. They have examined the human brains from the cadavers of normal and schizophrenia people using electron microscope. The microscopic images have showed the presence of rod-shaped bacteria in the brain samples of both normal and diseased brains. They even could able to notice the bacterial organs like nucleoid, ribosomes, vacuoles and capsule in those images. The scientific community got excited by this discovery. 

After we die, the gut bacteria can spread to other parts of our body including brain. In order to prove their discovery was not caused by the bacterial contamination after the death, the scientists examined the brains of mice. They sacrificed the mice and immediately took their brain samples. When they observed those mice brain samples under microscope, they found the presence of bacteria in them. To prove further, they collected brain samples from the mice which were specially grown in the germ-free environment. They found no bacteria in the brains of ‘germ-free’ mice. These findings indicate that bacteria may live in brain as like in gut. The bacterial phyla (Firmicutes, Proteobacteria and Bacteroidetes) they found using RNA sequencing are commonly live in our gut. But, they still have to find out how the bacteria enters the brain. 

(Human brains. Picture Courtesy: Prylarer, Pixabay)

The ‘Science’ magazine has reported an interesting story behind this wonderful discovery. According to ‘Science’, the lead researcher of this discovery, Courtney Walker found some rod-shaped objects in the brain samples five years ago. When Walker reported her discovery to her boss neuroanatomist Rosalinda Roberts, she rejected that the objects were not bacteria. Walker was enthusiastic about her discovery and continued to work on it. Finally, a bacteriologist confirmed them that they have actually found bacteria in brain. 

As mentioned earlier, this is a preliminary study. They have to examine more brains to support this discovery. There is no doubt that other research teams might have already started to do similar research on human brains.