Using DNA sequencing, researchers have examined bacteria in post-mortem brains from patients with Alzheimer’s disease. Their findings indicate increased bacterial populations and different proportions of specific bacteria in Alzheimer’s, compared with healthy brains. These findings may support evidence that bacterial infection and inflammation in the brain could contribute to Alzheimer’s disease.

Alzheimer’s disease causes neurons to die and break down, and involves high levels of a peptide called amyloid and aggregations of a protein called tau. However, scientists are coming to appreciate that inflammation may also play a role.

Bacterial infection may be one cause of inflammation, as well as certain genetic risk factors which can impact the inflammatory response. The brain is normally sealed behind specialized blood vessels that make it very difficult for things like bacteria in the blood to enter. However, at least one of the genetic risk-factors for Alzheimer’s disease may cause these blood vessels to lose some of their integrity, which could allow bacteria to enter and colonize the brain.

The research team analyzed eight Alzheimer’s and six healthy brain samples from a brain bank using a technique called next generation sequencing (NGS) to detect specific bacterial genes. They found that the Alzheimer’s brains contained different proportions of specific bacteria compared with the healthy brains, showing at least a tenfold higher ratio “Comparing the bacterial populations showed at least a tenfold higher overall ratio of Actinobacteria (mostly P. acnes) to Proteobacteria in the Alzheimer’s brain compared with the healthy brain.

Researchers were surprised to find that there also appeared to be more bacteria in the Alzheimer’s brains, an apparent 7-fold increase in bacterial sequences above that seen in the healthy brains.

The team caution that the NGS method does not directly indicate actual bacterial numbers, and further work will be required to confirm that bacteria play an active role in Alzheimer’s disease. Quantitative studies on bacterial presence and larger numbers of brain samples are required.

Paper: “Bacteria found in Alzheimer’s brains: Brains from patients with Alzheimer’s disease show changes in bacterial populations compared with healthy brains”
Reprinted from materials provided by Frontiers.