Germs in your brain

Did you know that there are GERMS in our brains?
Yeah, science can’t grow a single one of them, but they found DNA fingerprints of numerous bacteria.
These indigenous, resident bacteria, are killed by antibiotics that cross the blood brain barrier.
We have absolutely no idea what the impact of that is. Could be dementia, Alzheimer’s, anxiety, serotonin synthesis defects, and any other chemical imbalance. 
Equally interestingly, the body shows no immune response to those bacteria. That would suggest that they BELONG there. And what does that tell us? 
Since we don’t know anything about 99% of the germs in our bodies, how do we know that some of the medicines that we take such as blood pressure medicine or cholesterol pills aren’t killing or at least inhibiting specific germs.  
If we already KNOW that there are germs that manufacture and secrete various hormones and important biological compounds, then, of the literally 99% of the germs in our body that we can’t grow, and cannot study (besides their DNA fingerprinting), how many of those germs are beneficial or even essential to us? 
Taking a educated, scientific guess, I would bet my net-worth, that American neuropathies, auto immune disorders, generalized anxiety, inflammatory, bowel diseases,  even Alzheimer’s and certain forms of dementia, Parkinson’s are caused by the ABSENCE of certain, Neuro-supportive, beneficial bacteria.
These are conditions that are almost never reported in populations that do not get antibiotics, weather, by choice, geography, or economic factors.
It’s probably actually healthier to be poor, Amish, or an Eskimo.