APP and Alzheimer disease: Given that we identified significant differences in microbial abundance between APP/PS1 mice and wild-type control mice at the early stages (i.e., 1–3 months) when Aβ plaque accumulation and microglial activation have not occurred in the cerebral cortex, our results suggest that alteration of the gut microbiome profile occurs prior to amyloidosis and plaque-localized microglial activation in the brain of AD model mice.