High Throughput Sequencing Detects Gingivitis and Periodontal Oral Bacteria in Alzheimer's Disease Autopsy Brains

Abstract

The sporadic form of Alzheimer’s disease (AD) is the most common form of dementia characterized microscopically by the presence of amyloid-beta (Aβ) plaques and tau neurofibrillary tangles with the clinical presentation of cognitive deficit. Its etiology remains obscure. The cited literature from epidemiological studies suggests the presence of gingivitis and periodontitis almost double the risk for AD over a 10-year period. This feasibility study used 16S rDNA high throughput sequencing to evaluate the bacterial components of the oral microbiome in snap-frozen human AD and non-AD control brains. Specimens (n=20), 10 from AD brains and 10 from non-AD age-matched brains were subjected to molecular barcoding “blindly” with high throughput sequencing. Initial PCR treatment, using 14 different primer sets separately and in combination, identified 4 (40%) positive samples in the AD-group and 6 (60%) positive samples in the non-ADgroups. with bacterial species associated with the oral and the gastrointestinal tract. Brain cell lysates were validated for the presence of bacterial peptidoglycan and showed 8 out of 10 brains to be positive for this universal bacterial protein in both the AD and non-AD groups. Actinomycetales and Prevotella (bacterial marker for gingivitis) and Treponema and Veillonella, (periodontitis) were present exclusively in the AD group.This study confirmed Actinomycetales and Bacteroidales (Treponema and Veillonella species) were exclusively isolated from AD brain tissue, and supports other epidemiological studies which demonstrate gingivitis and periodontal disease to be associated with AD.