Andrii Vodolazhskyi/

Brains With Alzheimer's Have More Bacteria Than Healthy Ones, Says New Study

19 JULY 2017

New research shows bacteria that break through the brain's defences and infected neurons could play a role in the onset of Alzheimer's, giving experts a better understanding of the disease and ways we could treat it.


Scientists studying brains from deceased donors found variations in bacteria types and numbers between the healthy brains and those with Alzheimer's – and that could be key to figuring out how Alzheimer's starts.

Now the researchers, from the University of Bristol in the UK, think there could be a link between these bacteria populations and the neuroinflammation that has previously been connected to the development of the disease.

"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 one of the researchers, David Emery.

"Neuroinflammation in the brain may be a reaction to the presence of bacteria."

Using DNA sequencing to analyse the bacteria genes in the post-mortem brains, the team looked at eight samples from brains affected by Alzheimer's and six samples from healthy brains.

Overall the diseased brains showed at least a tenfold higher ratio of Actinobacteria to Proteobacteria. What's more, there were more bacterial sequences in the Alzheimer's brains overall.

The technique used here hints at rather than directly showing bacterial numbers, but it's a good basis for further research into any potential link between infection and Alzheimer's.


The bacterial species identified included those associated with the skin, mouth, and nose.

"Previous studies looking at bacteria in the Alzheimer's brain have primarily investigated specific bacterial species," explains one of the team, Shelley Allen.

"We wanted to use an unbiased method to obtain the fullest overview possible of the entire bacterial population."

It's not the first time that scientists have suggested a link between bacteria and Alzheimer's, though as yet there's no consensus on exactly what's happening. The problem is that much of the disease remains a mystery – which is why research like this is so helpful.

Now we have evidence that brains hit by Alzheimer's tend to have "strikingly large bacterial loads" in the words of the researchers – though they're quick to point out that much more detailed and larger studies are required to pin down a link.

We do know Alzheimer's affects 1 in 10 people over the age of 65, and the leading hypothesis is that brain cells are killed off by abnormal protein fragments known as plaques and tangles.

Keeping active, maintaining a healthy sleep pattern, and stimulating your mind are all ways in which you can try and reduce the risk of Alzheimer's, but as yet there's no cure. Let's hope this new research leads to further advances in treatment.

The research has been published in Frontiers in Aging Neuroscience.