Bacteria found in Alzheimer's brains

July 17, 2017
PET scan of a human brain with Alzheimer's disease. Credit: public domain

Researchers in the UK have used DNA sequencing to examine bacteria in post-mortem brains from patients with Alzheimer's disease. Their findings suggest increased bacterial populations and different proportions of specific bacteria in Alzheimer's, compared with healthy brains. The findings may support evidence that bacterial infection and inflammation in the brain could contribute to Alzheimer's disease.

Alzheimer's is a neurodegenerative disease that results in cognitive decline, and eventually death. In the brain, the 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.

"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 David Emery, a researcher from the University of Bristol, and an author on the study, which was recently published in Frontiers in Aging Neuroscience.

So, what's causing this inflammation? Some genetic risk-factors for Alzheimer's disease can have effects on the inflammatory response, but infection may also play a role. "Neuroinflammation in the brain may be a reaction to the presence of bacteria," says Emery. 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 set out to discover if there were any differences in the types of bacteria present in brains from Alzheimer's disease patients and healthy brains. "Previous studies looking at bacteria in the Alzheimer's brain have primarily investigated specific bacterial species," explains Shelley Allen, another researcher involved in the study. "We wanted to use an unbiased method to obtain the fullest overview possible of the entire in the Alzheimer's brain, and compare these results with those from a healthy aged brain."

The researchers analyzed eight Alzheimer's and six healthy brain samples from a brain bank, where people donate their brains after death for medical research. They used a technique called next generation sequencing (NGS) to detect specific bacterial genes. "NGS technology allows millions of these DNA molecules to be sequenced at the same time, providing an unbiased overview of a complex bacterial population," explains Allen.

They found that the Alzheimer's brains contained different proportions of specific bacteria compared with the healthy brains. "Comparing the bacterial populations showed at least a tenfold higher ratio overall of Actinobacteria (mostly P. acnes) to Proteobacteria in the Alzheimer's brain compared with the healthy brain," says Emery.

However, the researchers were surprised to find that there also appeared to be more bacteria in the Alzheimer's brains. "Unexpectedly, Alzheimer's brains gave on average an apparent 7-fold increase in bacterial sequences above that seen in the healthy brain," says Allen. "The healthy brains yielded only low levels of bacterial sequences, consistent with either a background signal or normal levels present in the blood stream in brain tissue."

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. "We need quantitative studies on the bacterial presence in the brain," says Allen. "Larger numbers of samples are required, and future studies should also investigate if are involved in other neurodegenerative diseases involving neuroinflammation."

Explore further: Gram-negative bacteria may influence Alzheimer's disease pathology

More information: David C. Emery et al, 16S rRNA Next Generation Sequencing Analysis Shows Bacteria in Alzheimer's Post-Mortem Brain, Frontiers in Aging Neuroscience (2017). DOI: 10.3389/fnagi.2017.00195

Related Stories

Gram-negative bacteria may influence Alzheimer's disease pathology

November 30, 2016
For the first time, researchers have found higher levels of Gram-negative bacteria antigens in brain samples from late-onset Alzheimer's disease patients. Compared to controls, patients with Alzheimer's had much higher levels ...

Study suggests possible new target for treating and preventing Alzheimer's

December 1, 2016
A new scientific discovery may provide a future avenue for treatment and prevention of Alzheimer's disease.

Abnormal brain protein may contribute to Alzheimer's disease development

September 30, 2016
A recently-recognized pathologic protein in the brain may play a larger role in the development of clinical Alzheimer's disease dementia than previously recognized, according to a study by researchers at Rush University Medical ...

Gut bacteria may play a role in Alzheimer's disease

February 10, 2017
New research from Lund University in Sweden has shown that intestinal bacteria can accelerate the development of Alzheimer's disease. According to the researchers behind the study, the results open up the door to new opportunities ...

New strategy may help combat Alzheimer's disease

March 14, 2017
Researchers have uncovered a mechanism that helps block the accumulation of proteins involved in Alzheimer's disease. Tapping into this natural process may therefore help prevent or treat the condition.

Research points to new treatment strategy against Alzheimer's disease

September 7, 2016
New research suggests that Alzheimer's disease may trigger increased expression of an enzyme called lysozyme, which attempts to counteract amyloid build-up in the brain.

Recommended for you

Lifestyle changes to stave off Alzheimer's? Hints, no proof

July 20, 2017
There are no proven ways to stave off Alzheimer's, but a new report raises the prospect that avoiding nine key risks starting in childhood just might delay or even prevent about a third of dementia cases around the world.

Blood test identifies key Alzheimer's marker

July 19, 2017
A new study led by researchers at Washington University School of Medicine in St. Louis suggests that measures of amyloid beta in the blood have the potential to help identify people with altered levels of amyloid in their ...

Steering an enzyme's 'scissors' shows potential for stopping Alzheimer's disease

July 19, 2017
The old real estate adage about "location, location, location" might also apply to the biochemical genesis of Alzheimer's disease, according to new research from the University of British Columbia.

Brain scans may change care for some people with memory loss

July 19, 2017
Does it really take an expensive brain scan to diagnose Alzheimer's? Not everybody needs one but new research suggests that for a surprising number of patients whose memory problems are hard to pin down, PET scans may lead ...

Can poor sleep boost odds for Alzheimer's?

July 18, 2017
(HealthDay)— Breathing problems during sleep may signal an increased risk for Alzheimer's disease, a trio of studies suggests.

Hearing is believing: Speech may be a clue to mental decline

July 17, 2017
Your speech may, um, help reveal if you're uh ... developing thinking problems. More pauses, filler words and other verbal changes might be an early sign of mental decline, which can lead to Alzheimer's disease, a study suggests.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.