Abstract
Tongue microbiota are a dominant source of oral microbial populations that are ingested with saliva, and therefore careful attention is required for the maintenance of health of elderly adults, who are susceptible to aspiration of oral contents. This study aimed to investigate the variation in tongue microbiota among community-dwelling elderly adults. Following a dental examination, tongue coating was collected from a 15-mm-diameter circular area at the center of the tongue dorsum of 506 elderly adults aged 70 to 80 years inhabiting the town of Hisayama, Japan. The microbial composition and density were determined by a 16S rRNA gene sequencing approach using a next-generation sequencer and quantitative PCR analysis, respectively. Co-occurrence network analysis identified two cohabiting groups of predominant commensals, one of which was primarily composed of Prevotella histicola, Veillonella atypica, Streptococcus salivarius, and Streptococcus parasanguinis; these organisms have been previously associated with an increased risk of mortality due to pneumonia in the frail elderly. This bacterial group was more predominant in the elderly with fewer teeth, a higher plaque index, and more dental caries experience, whereas the total bacterial density was independent of these traits. A higher density of fungi was also observed in the elderly with these traits, as well as in individuals who wore dentures. These results suggest that elderly adults with poorer oral health swallow a more dysbiotic microbiota formed on the tongue.IMPORTANCE Aspiration of oral contents can lead to pneumonia, which is a major cause of death among elderly adults susceptible to swallowing impairments. Tongue microbiota are a dominant source of oral microbial populations that are ingested with saliva. This large-scale population-based study revealed variations in the tongue microbiota among community-dwelling elderly adults. The total bacterial density was independent of the conditions of teeth surrounding the tongue, whereas the microbiota composition, especially the relative abundances of predominant commensals, showed an association with tooth conditions. Our results demonstrate that the elderly with fewer teeth, poorer dental hygiene, and more dental caries experience constantly ingest more dysbiotic microbiota, which could be harmful for their respiratory health.
Highlights
Tongue microbiota are a dominant source of oral microbial populations that are ingested with saliva, and careful attention is required for the maintenance of health of elderly adults, who are susceptible to aspiration of oral contents
This study investigated the tongue microbiota status of 506 elderly adults aged 70 to 80 years (231 males and 275 females) inhabiting the town of Hisayama who received a dental examination during a health examination of Hisayama residents performed in 2016
To investigate the relationship between tongue microbiota status and dental conditions, this study focused on total bacterial density and richness, total fungal density, and the relative abundances of the operational taxonomic units (OTUs) corresponding to four bacterial groups: mutans streptococci (MS) and lactobacilli as typical dental caries-associated taxa (14 OTUs [Table 2]) [18], the abovementioned 10 periodontitis-associated taxa listed in a previous study (11 OTUs [Table 2]) [19], and the predominant bacteria in commensal group I (4 OTUs [Fig. 1B and 2]) and II (12 OTUs [Fig. 1C and 2])
Summary
Tongue microbiota are a dominant source of oral microbial populations that are ingested with saliva, and careful attention is required for the maintenance of health of elderly adults, who are susceptible to aspiration of oral contents. Co-occurrence network analysis identified two cohabiting groups of predominant commensals, one of which was primarily composed of Prevotella histicola, Veillonella atypica, Streptococcus salivarius, and Streptococcus parasanguinis; these organisms have been previously associated with an increased risk of mortality due to pneumonia in the frail elderly This bacterial group was more predominant in the elderly with fewer teeth, a higher plaque index, and more dental caries experience, whereas the total bacterial density was independent of these traits. The loose community structure and the desquamation of epithelial cells facilitate the release of resident microorganisms into the saliva [11] These features imply that careful attention should be given to the tongue microbiota in the elderly susceptible to swallowing impairments [12]. Increased tongue coating in edentulous elderly adults, scored by visual inspections, was associated with aspiration pneumonia [13] and febrile status [14]
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