The brains of people who die with The brains of people who die with

Could Infections, Bacteria Be Factors in Alzheimer’s Risk?

Son sitting with aging father with dementiaThe brains of people who die with Alzheimer’s contain different proportions of some bacteria than do the brains of people without the disease, according to a study published in the journal Frontiers in Aging Neuroscience.

The study used donations to a brain bank to compare the brains of eight people with Alzheimer’s to the brains of six people without signs of Alzheimer’s.

Bacterial Changes in Brains with Alzheimer’s

Previous research has found the brains of people with Alzheimer’s often show signs of inflammation. Inflammation is linked to a wide range of health problems and might cause neural degeneration in those with Alzheimer’s.

Researchers do not know what causes neuroinflammation. It is possible that several factors are at play. Genetic risk factors for the disease might alter the brain’s inflammatory response. Infections can also cause inflammation, suggesting bacteria might play a role in Alzheimer’s.

Researchers sought a full analysis of the bacterial content of the donated brains. Using a technique called next generation sequencing (NGS), which detects specific bacterial genes, they sequenced millions of DNA molecules and produced a comprehensive overview of each brain’s bacterial contents.

People who died with Alzheimer’s had brain concentrations of specific types of bacteria at least 10 times as high as those without Alzheimer’s. Healthy brains showed lower overall concentrations of bacteria.

Link Between Infections and Alzheimer’s

Other research supports the conclusion that infections may play a role in Alzheimer’s-related neuroinflammation. A study of mice found the amyloid plaques characteristic of Alzheimer’s and the biofilm produced by some gut bacteria may elicit an identical immune response. This offers another explanation for the chronic inflammation seen in most Alzheimer’s brains.

A 2016 editorial published in the Journal of Alzheimer’s Disease calls for more investigation into potential infectious causes of Alzheimer’s. The editorial points to more than 100 studies finding a link between the herpes virus HSV1 and Alzheimer’s.

Several studies suggest people with Alzheimer’s may also be more likely to have fungal infections.


  1. Alonso, R., Piso, D., Marina, A. I., Morato, E., Rabano, A., & Carrasco, L. (2014). Fungal infection in patients with Alzheimer’s disease. Journal of Alzheimer’s Disease. doi:10.3233/JAD-132681
  2. Alzheimer’s-causing amyloid and bacteria trigger same immune response. (n.d.). Retrieved from
  3. Bacteria found in Alzheimer’s brains. (2017, July 17). Retrieved from
  4. Emery, D. C., Shoemark, D. K., Batstone, T. E., Waterfall, C. M., Coghill, J. A., Cerajewska, T. L., . . . Allen, S. J. (2017). 16S rRNA next generation sequencing analysis shows bacteria in Alzheimer’s post-mortem brain. Frontiers in Aging Neuroscience, 9. doi:10.3389/fnagi.2017.00195
  5. Itzhaki, R. F., Lathe, R., Balin, B. J., Ball, M. J., Bearer, E. L., Braak, H., . . . Whittum-Hudson, J. A. (2016). Microbes and Alzheimer’s disease. Journal of Alzheimer’s Disease, 51(4), 979-984. doi:10.3233/jad-160152

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  • val

    July 27th, 2017 at 1:06 PM

    While these seem like valid points I think that the study has to get a little wider reaching than simply looking at 14 brain specimens.

  • Jonas

    July 28th, 2017 at 9:09 AM

    There are so many underlying things that could effect whether or not one will develop Alzheimer’s. I am glad that researchers are starting to look at things from a different perspective, going a little bit outside of the box of what you would normally expect. I think that it is with this kind of innovation and thinking that eventually we will learn the real causes and in addition will help to develop a cure.

  • Teddy

    July 31st, 2017 at 12:21 PM

    lots of mights and mays in here
    i know that that is a good place to start
    but you would hope that we would have had something a little more definitive by now
    until then
    i guess we just keep on keeping on
    hoping that the big breakthrough is right around the next corner

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