Analysis of oral microbiome diversity in Alzheimer’s disease patients from Kazakhstan

Background
Recent studies have suggested that periodontal disease and alterations in the oral microbiome may be associated with cognitive decline and the development of Alzheimer’s disease (AD). Here, we report a pilot case-control study of oral microbiota diversity in AD patients in comparison with healthy seniors from the Central Asian region.

Method
We have characterized the bacterial taxonomic composition of the oral microbiome from AD patients (n = 69) compared to the healthy group (n = 72) using 16S ribosomal RNA sequencing.

Result
Our analysis showed that the oral microbiome of AD has a higher microbial diversity. More importantly, differences across taxonomic groups are distinguished by the diversity of opportunistic flora in the AD group. We identified differences between phyla and genera in bacterial abundance, including a decrease in the Firmicutes/Bacteroidetes ratio in the microbiome of AD participants. LEfSe allowed determining an enrichment at the Genus Pseudomonas, Prevotella_9, UCG_002, Esherichia_Shigella, Mogibacterium, Ralstonia, and Bergeyella in the AD group. A significant increase in the genus Mogibacterium, which is also associated with an aggressive form of periodontitis and type 2 diabetes mellitus, was revealed. The genus Ralstonia are commensal representatives of the oral microbiome, but with a reduced immune system they exhibit pathogenic properties and are associated with a higher risk of mortality in hematological malignancies and hereditary disorders of hematopoiesis. One of the least studied Bergeyella spp, which is a representative of the oral microbiome of dogs, cats, and pigs, therefore, it is isolated on contact and is associated with the risk of preterm birth, as well as the development of endocarditis in a weakened body.

Conclusion
Our results confirm that the oral microbiome is a potential target for therapeutic intervention in AD. However, a comprehensive picture of the full composition of the oral microbiome in patients with AD requires further investigation.