Profiling the oral microbiomes in patients with Alzheimer's disease.

OBJECTIVES: To analyse the characteristics of the oral microbiomes and expected to find biomarkers about Alzheimer's disease (AD). SUBJECTS AND METHODS: AD patients (n = 26) and cognitive intact people (n = 26) were examined for cognition, depression, oral health and collected saliva and gingival crevicular fluid (GCF) in the morning. Full-length 16S rRNA gene was amplified and sequencing was performed using the PacBio platform. RESULTS: The predominant bacterium of salivary microbiome and periodontal microbiome from AD patients was Streptococcus oralis and Porphyromonas gingivalis, respectively. With respect to ß diversity analysis, there was a significance difference in periodontal microbiome between AD patients and cognitively intact subjects. The relative abundance of Veillonella parvula significantly increased in oral microbiomes from AD patients. Interestingly, the dominant species were different between early-onset AD and late-onset AD patients. Moreover, the predominant species were changed as the clinical severity of AD. Furthermore, the correlation analysis revealed that V. parvula was associated with AD in both saliva and GCF and that P. gingivalis was associated with AD only in GCF. CONCLUSIONS: In this study, the microbiome community of oral microbes was altered in AD patients and periodontal microbiome was sensitive to cognition changes. Moreover, V. parvula and P. gingivalis were associated with AD.