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Alzheimer’s Brains Have 7 Times More Bacteria Than Healthy Brains

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Many more bacteria have been found in the brains of Alzheimer’s patients as opposed to those of healthy people, shows a new study published in Frontiers in Aging Neuroscience.

Alzheimer’s disease & Increased Bacterial Populations

Alzheimer’s disease, a neurodegenerative condition characterised by loss of memory and cognitive function, might be linked with bacterial infection in the brain, and inflammation, suggests new research conducted by scientists from the UK. The team recovered samples of bacteria from the brains of 8 deceased Alzheimer’s patients, and examined them using DNA sequencing. They compared the results with the brain samples from 6 healthy people. The scientists found not only more bacterial populations in the diseased brains but also a different proportion of certain species of bacteria when compared with brains from healthy people.

It is to be noted that the brains used for the study came from a brain bank whereby people donate their brains after death for research purposes.

Brain cross sections. Alzheimer’s brain compared with healthy brain: the former is characterised by shrinking of the brain tissue.

Bacterial Infection & Inflammation

Previous studies show that Alzheimer’s disease involves an accumulation of a peptide known as amyloid and a protein called tau; the condition is also associated with the death of neurones. Inflammation might have to be added to the list, say the researchers of the new paper.

“Alzheimer’s brains usually contain evidence of neuroinflammation, and researchers increasingly think that this could be a possible driver of the disease, by causing neurons in the brain to degenerate,” says study author David Emery.

This inflammation might have a genetic cause that makes certain people more susceptible to it. The new findings now suggest that bacterial infection might also be responsible for the inflammator response.

Emery explains that bacteria present in the brain might trigger neuroinflammation in the organ. Normally, the brain is protected from the influx of bacteria by a barricade of blood vessels. However, the genetic risk-factors associated with Alzheimer’s are thought to adversely affect these blood vessels—this might, then, enable the entry of bacteria in the brain.

Different Amount & Ratio of Bacterial Populations

The bacterial populations were thoroughly analysed with a new technique called next generation sequencing (NGS) which allowed for the detection of specific bacterial genes. The researchers were, thus, able to determine that Alzheimer’s brains had more bacteria (around 7 times more), with a “tenfold higher ratio overall of Actinobacteria (mostly P. acnes) to Proteobacteria”, says Emery.

The authors add that quantitative studies will now need to be done because their technique does not actually show the bacterial numbers.

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