Subgingival microbiome at different levels of cognition

Abstract

Oral health and declining cognition may have a bi-directional association. We characterized the subgingival microbiota composition of subjects from normal cognition to severe cognitive decline in two cohorts. Memory and Periodontitis (MINOPAR) include 202 home-living participants (50-80 years) in Sweden. Finnish Oral Health Studies in Older Adults (FINORAL) include 174 participants (≥65 years) living in long-term care in Finland. We performed oral examination and assessed the cognitive level with Mini Mental State Examination (MMSE). We sequenced the 16S-rRNA gene (V3-V4 regions) to analyse the subgingival bacterial compositions. The microbial diversities only tended to differ between the MMSE categories, and the strongest determinants were increased probing pocket depth (PPD) and presence of caries. However, abundances of 101 taxa were associated with the MMSE score. After adjusting for age, sex, medications, PPD, and caries, only eight taxa retained the significance in the meta-analyses of the two cohorts. Especially Lachnospiraceae [XIV] at the family, genus, and species level increased with decreasing MMSE. Cognitive decline is associated with obvious changes in the composition of the oral microbiota. Impaired cognition is accompanied with poor oral health status and the appearance of major taxa of the gut microbiota in the oral cavity. Good oral health-care practices require special deliberations among older adults.

Keywords: Oral health; cognition; cognitive decline; mini mental state examination (MMSE); older adults; subgingival microbiome.

Figure 1.

MMSE categories in MINOPAR and FINORAL. MINOPAR (n = 202) and FINORAL (n = 174) participants were divided into subgroups according to the MMSE score. The scores for normal cognition, and mild, moderate and severe decline of cognition were 25–30, 20–24, 10–19, and 0–9.

Figure 2.

Alpha diversity of the oral microbiome in the MMSE categories. MINOPAR (n = 202) and FINORAL (n = 174) participants were divided into subgroups according to the MMSE score as normal, mild, moderate, and severe cognitive decline. Alpha diversity as observed richness and Shannon index were calculated for the subgingival microbiome composition in both cohorts. p-values for the significance of the difference between the MMSE groups are shown. The box plots present median (x), mean (line), IQR (box), and 95% CI (error bars).

Figure 3.

Meta-analyses of the significant OTUs. the forest plots display the results of the final random effects models produced by meta-analyses of all significant taxa of either cohort, adjusted for age, sex, number of medications, PPD≥6 mm and presence of caries. Effect size and 95% CI are shown separately for MINOPAR, FINORAL, and their meta-analyses.