I find very interesting the idea that intestinal microbiota might influence brain development and behaviour. There are research groups or studies that explore a link between the gut miocrobioma and dementia?
The group of Marco Prinz (Freiburg) have published a paper this year linking between microbiota and brain microglia. Check it out it might give you some hints. Host
microbiota constantly control maturation
and function of microglia in the CNS. Nature neuroscience.
Very interesting however the problem seems to manifest in how individuals deal with the inflammation of invaders to the brain on a very individual way.