Oral Microbiota Changes in Elderly Patients, an Indicator of Alzheimer’s Disease Original paper

What was studied?

This study investigated oral microbiota Alzheimer’s disease associations by examining dental plaque microbiota in elderly individuals with Alzheimer’s disease (AD) compared with cognitively normal controls. Using full-length 16S rDNA sequencing via the PacBio SMRT platform, researchers characterized microbial diversity, taxonomic composition, and taxa with discriminatory value between groups. The aim was to determine whether specific shifts in the oral microbiome—particularly increases in cariogenic and inflammation-linked bacteria—could serve as potential biomarkers for AD detection. The analysis integrated sequencing results with clinical measures, including missing teeth, plaque burden, DMFT index, and cognitive scores to explore interactions between oral health status and microbiota imbalance.

Who was studied?

The study included 35 Taiwanese participants: 17 clinically diagnosed AD patients and 18 age-matched elderly controls without cognitive complaints. All participants were native, middle-class individuals who met the inclusion criteria and had no recent antibiotic exposure. AD diagnoses were confirmed based on the National Institute on Aging–Alzheimer’s Association criteria. Dental plaque samples were collected from supragingival surfaces by trained dentists. Clinical assessments included the Clinical Dementia Rating (CDR), Mini–Mental State Examination (MMSE), missing teeth count, DMFT index, and plaque weight. AD participants showed significantly more missing teeth and greater plaque accumulation, offering a distinct oral health context for microbiome comparisons.

Most important findings

Across pages 5–8 (figures and tables), AD patients exhibited significantly reduced oral microbial diversity, reflected in lower OTU counts and fewer unique sequence tags. Key taxonomic differences included elevated Firmicutes, increased Firmicutes/Bacteroidetes (F/B) ratio, and higher prevalence of Lactobacillales, Streptococcaceae, Actinomycetaceae, and Veillonellaceae. Conversely, taxa associated with periodontal health or anti-inflammatory potential—such as Fusobacterium, Fusobacteriaceae, Cardiobacterium, Porphyromonadaceae, and Proteobacteria—were significantly reduced. These shifts suggest dysbiosis characterized by increased cariogenic and inflammation-related bacteria alongside loss of protective genera. The LEfSe analysis (page 8) further highlighted Streptococcus, Lactobacillus, Shuttleworthia, and Bacilli as enriched biomarkers in AD, while Fusobacterium, Alloprevotella, and Porphyromonadaceae characterized controls.

Key implications

The study strengthens evidence that oral dysbiosis may contribute to AD-related neuroinflammation. Elevated Firmicutes and Streptococcaceae, combined with reduced Fusobacterium, point toward a microbial signature potentially linked to both impaired oral health and neurodegenerative processes. The increased F/B ratio (>1), associated with systemic inflammation, suggests that plaque-derived bacteria could influence brain pathology via inflammatory mediators or by translocation across compromised mucosal or vascular barriers. These findings indicate that profiling the oral microbiome—especially through long-read sequencing—may support early, non-invasive AD risk assessment. Moreover, microbial patterns implicate specific genera as candidates for microbiome-based diagnostic tools or future therapeutic targets.

Citation

Wu YF, Lee WF, Salamanca E, Yao WL, Su JN, Wang SY, Hu CJ, Chang WJ. Oral Microbiota Changes in Elderly Patients, an Indicator of Alzheimer’s Disease. International Journal of Environmental Research and Public Health. 2021;18(8):4211. doi:10.3390/ijerph18084211