There are differences in Alzheimer's patients and their gut microbiota, and that's been verified by many groups now. Prior research has shown that when you make changes in the gut microbiota of Alzheimer model mice, you in turn have effects on the pathology of the hallmarks of Alzheimer's - amyloid plaques and tau accumulation.
There is still so much to learn about the connection between our gut microbiome and chronic disease. University labs make important discoveries in this area.