  Alzheimer's disease is the most common form of dementia in the western world,
however there is no cure available for this devastating neurodegenerative
disorder. Despite clinical and experimental evidence implicating the intestinal
microbiota in a number of brain disorders, its impact on Alzheimer's disease is
not known. We generated a germ-free mouse model of Alzheimer's disease and
discovered a drastic reduction of cerebral Ab amyloid pathology when compared
to control Alzheimer's disease animals with intestinal microbiota. Sequencing
bacterial 16S rRNA from fecal samples revealed a remarkable shift in the gut
microbiota of conventionally-raised Alzheimer's disease mice as compared to
healthy, wild-type mice. Colonization of germ-free Alzheimer mice with
harvested microbiota from conventionally-raised Alzheimer mice dramatically
increased cerebral Ab pathology. In contrast, colonization with microbiota from
control wild-type mice was ineffective in increasing cerebral Ab levels. Our
results indicate a microbial involvement in the development of Alzheimer's
disease pathology, and suggest that microbiota may contribute to the
development of neurodegenerative diseases.
