Gut and Oral microbiota alterations in patients with Alzheimer's disease

Alzheimer's disease (AD) is one of the most frequently diagnosed neurodegenerative disorders worldwide. However, the etiopathogenesis of this devastating disease is not completely understood. Recent studies suggest that alterations in the oral and gut microbiome may contribute to amyloid deposition, yet the microbial communities associated with AD have not been fully characterized in humans and little is known about the microbial composition in the course of the disease. Towards this end, we characterized the bacterial taxonomic composition of fecal and swab samples from participants in different stages of AD (AD, MCI, at risk).Our analyses revealed that the gut microbiota of AD participants has decreased microbial diversity and is compositionally distinct from control age- and sex-matched individuals. We identified phylum- through genus-wide differences in bacterial abundance including increased Firmicutes, increased Bacteroidetes, and decreased Roseburia in the gut microbiota of AD participants. Whereas significantly higher abundance of Porphyromonas and members of the Proteobacteria, especially Haemophilus, Neisseria and Actinobacillus was observed in the oral microbiota of AD patients. Furthermore, we observed correlations between levels of differentially abundant genera and cerebrospinal fluid (CSF) biomarkers of AD. These findings add AD to the growing list of diseases associated with gut and oral microbial alterations, as well as suggest that gut and oral bacterial communities may be a target for therapeutic intervention.