High number of distinct OTUs assigned to Prevotellaceae from both dementia and non-dementia samples. The number of distinct OTUs that are identified in four families that represent 2/3 of the total sequences were averaged for all samples and shown. Error bars represent standard error. Asterisk represents statistically significant difference by analysis of variance followed by Tukey’s multiple comparison test (P < 0.05). OTU, Operational Taxonomic Units.