Oral microbiota changes in elderly patients, an indicator of Alzheimer’s disease Original paper

What was studied?

This study examined oral microbiota changes in elderly individuals with Alzheimer’s disease (AD), aiming to determine whether distinct microbial signatures in dental plaque could help identify AD. The focus keyphrase oral microbiota changes in Alzheimer’s disease appears throughout because the work centers on how plaque-associated bacteria shift in composition, richness, and diversity in relation to cognitive impairment. Using PacBio single-molecule real-time sequencing—a full-length 16S rRNA method—the authors characterized microbial profiles from supragingival plaque and compared AD participants with cognitively normal elderly controls. The investigation emphasized taxonomic differences, diversity metrics, and the presence of potential microbial biomarkers that could contribute to neuroinflammatory pathways relevant to AD.

Who was studied?

The study enrolled 17 elderly patients with Alzheimer’s disease and 18 cognitively normal elderly controls, all middle-class Taiwanese adults. AD diagnoses were made according to National Institute on Aging–Alzheimer’s Association criteria. Participants with recent antibiotic use, oral cancer, or other neurological disorders were excluded. Clinical assessments included Mini–Mental State Examination scores, Clinical Dementia Rating, number of missing teeth, plaque weight, and DMFT indices. Plaque samples were collected by trained dentists, and DNA was extracted for sequencing. The AD group had significantly more missing teeth and higher plaque accumulation, providing a clinically relevant context for examining microbial dysbiosis.

Most important findings

The central finding was a pronounced reduction in oral microbial diversity in the AD group. Alpha-diversity metrics (Shannon and Simpson indices) and observed species counts were consistently lower. Taxonomic shifts were pronounced: AD participants exhibited increased Firmicutes, Lactobacillales, Streptococcaceae, Actinomycetaceae, and Veillonellaceae, while Fusobacteria, Fusobacteriales, Cardiobacteriales, Porphyromonadaceae, and Fusobacterium were depleted. The Firmicutes/Bacteroidetes ratio—often interpreted as an inflammation-associated marker—was significantly elevated. The LEfSe analysis highlighted specific bacterial biomarkers enriched in AD: Bacilli, Lactobacillales, Streptococcaceae, Streptococcus, and Shuttleworthia. Controls were enriched with Fusobacterium, Porphyromonadaceae, Alloprevotella, and Cardiobacterium. The study also found strong correlations between cognitive impairment scores and both plaque burden and microbial compositions, particularly the proportion of Firmicutes. These microbial alterations suggest a dysbiotic environment consistent with increased inflammatory potential.

Key implications

The findings indicate that oral microbiota changes in Alzheimer’s disease may contribute to or mirror neuroinflammatory processes through reduced diversity and expansion of pro-inflammatory or cariogenic taxa. The enrichment of Lactobacillales and Streptococcaceae—bacteria known for cariogenic and amyloidogenic potential—combined with the depletion of Fusobacterium and other commensals, reflects a shift toward dysbiosis that may increase systemic inflammatory signaling. From a clinical perspective, these results support the value of monitoring oral microbial signatures as adjunctive biomarkers for early AD detection. They also reinforce the importance of oral hygiene interventions to mitigate inflammatory burden in cognitively vulnerable populations. Full-length 16S sequencing shows promise as a diagnostic tool, although cost and confounding factors warrant further research.

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