Classifying dementia progression using microbial profiling of saliva

Abstract

Abstract Introduction There is increasing evidence linking periodontal infections to Alzheimer’s disease. Saliva sampling can reveal information about the host and pathogen interactions that can inform about physiological and pathological brain states. Methods A cross-sectional cohort of age-matched subjects (78) was segmented according to their chemosensory (University of Pennsylvania smell identification test; UPSIT) and cognitive scores (mini-mental score evaluation; MMSE and clinical dementia rating; CDR). Mid-morning saliva was sampled from each subject and processed for microbiome composition and cytokine analysis. Linear discriminant analysis (LDA) was used to unravel specific changes in microbial and immunological signatures and logistic regression analysis (LRA) was employed to identify taxa that varied in abundance among patients’ groups. Results Using olfaction we distinguish in the cognitively normal population a segment with high chemosensory scores (CNh, 27) and another segment with chemosensory scores (CNr, 16) as low as MCI (21) but higher than the AD group (17). We could identify stage-specific microbial signatures changes but no clear distinct cytokine profiles. Periodontal pathogen species as F. villosus decline with increasing severity of AD while opportunistic oral bacteria as L. Wadei shows a significant enrichment MCI. Conclusions: The salivary microbiome indicates stage-dependent changes in oral bacteria favoring opportunistic bacteria at the expenses of periodontal bacteria, while the inflammatory profiles remain mainly unchanged in the sampled population.