Development and establishment of oral microbiota in early life.

BACKGROUND: The oral microbiota has recently attracted attention owing to its association with oral and systemic diseases. Accordingly, gaining an understanding of oral microbiota development and the factors influencing it can contribute to preventing the establishment of dysbiotic oral microbiota and, eventually, oral microbiota-related diseases. HIGHLIGHT: In this review, we highlight the results of a longitudinal project focusing on oral microbiota development during early life. At 4 months of age, the oral microbiota of infants was found to differ considerably from the maternal oral microbiota, even though infants acquire oral bacteria from their mothers. At 18 months, although the infant microbiota is still not completely comparable with that of adults, from 4 to 18 months, there is a rapid phase of development, during which the microbial composition undergoes considerable change to a profile more similar to that in adults. During this development, the infant oral microbiota converges into two different profiles with adult-like traits, namely, Streptococcus salivarius- and Neisseria-dominant profiles. This divergence is strongly influenced by dietary habits, with a frequent intake of sweetened beverages being associated with an S. salivarius-dominant profile, which is suspected to be implicated in oral and systemic diseases. CONCLUSION: The foundation of the adult oral microbiota may be established by 18 months of age, and the developmental period from 4 to 18 months may be an appropriate period during which to modify the microbial balance to obtain a desirable healthy state. In particular, dietary habits during this period warrant close attention.

Oral-to-rectum microbial transmission in orthopedic patients without a history of intestinal disorders.

The enrichment of oral taxa in the gut has recently been reported as a notable alteration in the microbial balance in patients with intestinal disorders. However, translocation in populations without such diseases remains controversial. In this study, we examined 49 pairs of tongue and rectal samples collected from orthopedic patients without a history of intestinal disorders to verify the presence of oral taxa in the rectal microbiota. The bacterial composition of each sample was determined using 16S rRNA gene sequencing and amplicon sequence variant (ASV) analysis. Although the bacterial compositions of the tongue and rectal microbiota were distinctly different, tongue ASVs were detected in 67.3% of the participants and accounted for 0.0%-9.37% of the rectal microbiota. Particularly, Streptococcus salivarius, Fusobacterium nucleatum, and Streptococcus parasanguinis were abundant in the rectal microbiota. According to the network analysis, tongue taxa, such as S. salivarius and S. parasanguinis, formed a cohabiting group with Klebsiella pneumoniae and Alistipes finegoldii in the rectal microbiota. The total abundance of tongue ASVs in the rectal microbiota was significantly higher in participants with older age, hypertension, and proton pump inhibitor (PPI) use. Our study presents an extensive translocation of oral taxa to the rectum of a population without intestinal disorders and suggests that aging, hypertension, and PPI use are associated with an increased abundance of oral taxa and potential pathogenic bacteria in the rectal microbiota.

Establishment of tongue microbiota by 18 months of age and determinants of its microbial profile.

IMPORTANCE: Understanding the development of oral microbiota early in life and the factors that influence it is important for preventing the establishment of dysbiotic oral microbiota later in life. This study demonstrates that the tongue microbiota undergoes early development from 4 to 18 months of age and converges into two types of microbiota showing indications of adult characteristics, with either S. salivarius or Neisseria-dominance. Interestingly, their divergence was strongly determined by their weaning status and the dietary frequencies of sweetened beverages, snacks, and fruits, suggesting that dietary habits during this period might influence the establishment of the oral microbiota. These findings may contribute to the development of novel preventive strategies against oral microbiota-related diseases.

Association of second-hand smoke exposure, quantified by salivary cotinine, with dental caries in Japanese adolescents.

PURPOSE: Second-hand smoke has adverse effects on oral health. This cohort study used a multilevel approach to investigate the association of second-hand smoke exposure, as determined by salivary cotinine level, with dental caries in adolescents. METHODS: Data from 75 adolescents aged 11 or 12 years and 2,061 teeth without dental caries were analyzed in this study. Annual dental examinations to assess dental caries were conducted between 2018 and 2021. Salivary cotinine and Dentocult SM-Strip level were measured at baseline. Information on the smoking habits of parents, snack frequency, regular dental visits, and use of fluoride toothpaste was collected at baseline from parent-reported questionnaires. RESULTS: During the 3-year follow-up, dental caries was noted in 21 adolescents and 43 teeth. Participants exposed to parental smoking had higher salivary cotinine levels than those whose parents did not smoke. The multilevel Cox regression model showed that a high salivary cotinine level was associated with the incidence of dental caries, after adjusting for potential confounding factors (hazard ratio, 3.39; 95% confidence interval 1.08-10.69). CONCLUSION: This study suggests that the risk of dental caries is higher for adolescents who have high salivary cotinine levels attributable to second-hand smoke exposure.

Butyrate as a Potential Driver of a Dysbiotic Shift of the Tongue Microbiota.

The tongue dorsum is colonized by a stable microbiota, mostly comprising common commensal taxa. However, the predominance of each taxon varies among individuals. We hypothesized that equilibrium in the tongue microbiota is affected by exposure to butyrate in the oral fluid, which is reported to affect the growth of specific microorganisms. In this study, the bacterial composition of the tongue microbiotas of 69 male adults was determined via 16S rRNA gene sequencing to investigate its relationship to n-butyric acid concentration in oral rinse samples. The tongue microbiotas of individuals with a higher n-butyric acid level had higher relative abundances of Prevotella histicola, Veillonella atypica, and Streptococcus parasanguinis and lower relative abundances of Neisseria subflava and Porphyromonas pasteri. Subsequently, tongue microbiota samples collected from 12 adults were cultivated for 13 h in basal medium containing mucin and different concentrations of sodium butyrate (0, 0.8, 1.6, and 3.2 mM) to assess its effect on the growth of tongue microbiota organisms. The bacterial composition of the cultivated tongue microbiotas also demonstrated a significant gradual shift with an increase in sodium butyrate levels in beta-diversity analysis. N. subflava was significantly less predominant in the microbiota after cultivation with an increased addition of sodium butyrate, although no statistical difference was observed in the other aforementioned taxa. These results suggest that butyrate in the oral fluid is partially involved in the dysbiotic shift of the tongue microbiota. IMPORTANCE Oral microbial populations that are always ingested with saliva have attracted increasing attention because more oral microorganisms than previously known reach distal organs, such as the lungs and intestinal tract, thereby affecting our health. However, although such organisms are predominately derived from the tongue dorsum, the dynamics and determinants of the tongue microbiota composition remain unclear. This study demonstrated that exposure to butyrate could lead to a dysbiotic shift in the tongue microbiota using an observational epidemiological and microbiota cultivation approach. This result adds a new dimension to tongue microbiota ecology.

Yogurt product intake and reduction of tooth loss risk in a Japanese community.

AIM: To evaluate the longitudinal association between yogurt product intake and oral health in a population-based study. MATERIALS AND METHODS: This study included 1967 Japanese residents aged 40-79 years who underwent dental examinations in 2012. Among them, 1469 participants were followed up in 2017 for the incidence of tooth loss, which was defined as two or more teeth lost over 5 years. The intake of yogurt products, defined as yogurt and lactic acid beverages, was estimated using a semi-quantitative food frequency questionnaire. The composition of the salivary microbiota was evaluated. RESULTS: The Poisson regression model showed that a higher intake of yogurt products was negatively associated with the incidence of tooth loss (p for trend = .020), adjusted for potential confounding factors. Mediation analysis confirmed that periodontal condition partly mediated the effect of yogurt product intake on tooth loss, while dental caries experience did not. Additionally, we confirmed the association of a high intake of yogurt products with a low percentage of the salivary microbiota pattern, which was associated with poor oral health. CONCLUSION: These findings suggest that the intake of yogurt products is associated with a lower risk of tooth loss resulting from periodontal disease, probably via modulation of the oral microbiome composition.

High-Level Acquisition of Maternal Oral Bacteria in Formula-Fed Infant Oral Microbiota.

The influx of maternal oral microbes is considered to play an important role in the acquisition and development of infant oral microbiota. In this study, we examined tongue swab samples from 448 mother-infant pairs at 4-month checkups. The bacterial composition of each sample was determined using PacBio single-molecule long-read sequencing of the full-length 16S rRNA gene and the amplicon sequence variant (ASV) approach. Although the infant oral microbiota was distinctly different from the mother oral microbiota, ASVs shared with their biological mother accounted for a median relative abundance of 9.7% (range of 0.0 to 99.3%), which was significantly higher than that of ASVs shared with unrelated mothers. This shared abundance was strongly associated with the feeding method of infants rather than their delivery mode or antibiotic exposure, and formula-fed infants had higher shared abundance than exclusively breastfed infants. Our study presents strain-level evidence for mother-to-infant transmission of oral bacteria and suggests that colonization of maternal oral bacteria is higher in formula-fed infants. IMPORTANCE Acquisition of oral bacteria during infancy can affect the subsequent formation of stable oral microbiota. This study focused on the mother-to-infant transmission of oral bacteria, a major acquisition route of infant oral microbiota, and demonstrated that most infants acquired oral bacteria from their biological mother even at the single-nucleotide level. Our results also indicated that the occupancies of maternal oral bacteria in infant oral microbiota were associated with the feeding methods of infants. These data could increase understanding of the early development of oral microbiota in infants and its potential associations with oral microbiota-related diseases.

Baseline periodontal status and modifiable risk factors are associated with tooth loss over a 10-year period: Estimates of population attributable risk in a Japanese community.

BACKGROUND: This study aimed to examine whether modifiable risk factors can predict tooth loss over 10 years and estimate population attributable risk (PAR) for a combination of modifiable factors. METHODS: This longitudinal study included 1466 participants who underwent dental examinations in 2007 and 2017 and were aged 40 to 79 years at baseline. Periodontal conditions were assessed using the 2018 periodontal classification. Incident tooth loss was defined as ≥4 teeth lost over a 10-year period. We calculated the partial PAR (pPAR%) for tooth loss to estimate the combined effect of modifiable risk factors. RESULTS: Incidence of tooth loss was 17.5%. Directed acyclic graphs were used to identify risk factors for tooth loss. A logistic regression model showed that baseline periodontitis, dental caries experience, no regular dental visit, periodontal treatment, smoking, and obesity were associated with tooth loss after adjusting for covariates; pPAR% was 55.5% (95% confidence interval: 31.1% to 73.0%) in periodontitis Stage III to IV and 87.6% (50.4% to 97.4%) in the combination of all factors, respectively. The sex-stratified analysis showed that smoking and no regular dental visit in men and obesity in women were identified as potential risk factors for tooth loss. CONCLUSIONS: Modifiable factors accounted for most cases of incident tooth loss. Risk factors for tooth loss might differ by sex, suggesting that the appropriate approach for preventing tooth loss base on sex.

10-year trend of tooth loss and associated factors in a Japanese population-based longitudinal study.

OBJECTIVES: We examined the trend in the number of missing teeth in a Japanese community over a 10-year period and the potential associated explanatory factors. DESIGN: Prospective cohort study. SETTING: A population-based study conducted in 2007, 2012 and 2017 in Japan (Hisayama Study). PARTICIPANTS: Residents of a Japanese community aged 40-79 years undergoing dental examination in 2007 (n=2665), 2012 (n=2325) and 2017 (n=2285). OUTCOME MEASURES: The number of missing teeth, periodontal condition, dental caries experience, dental plaque index and oral health behaviours were evaluated each year. The longitudinal analysis of variation in these factors were assessed using mixed models. RESULTS: The age-adjusted and sex-adjusted mean number of missing teeth decreased with time (6.80 in 2007, 6.01 in 2012 and 4.99 in 2017). The mean clinical attachment level (CAL), prevalence of periodontitis and dental plaque index decreased over the study period, while dental caries experience slightly increased. The level of oral health behaviour increased over time. Poisson mixed models showed that changes in mean CAL and dental caries experience were positively associated with the change in the number of missing teeth over time. Linear mixed models showed that changes in dental plaque index and no regular dental visit were positively associated with changes in mean CAL. CONCLUSIONS: These findings suggest that a decreasing trend regarding the number of missing teeth in Japan might be associated with improvements in the periodontal condition due to changes in oral hygiene level and oral health behaviour.

Clinical utility of subgingival plaque-specific bacteria in salivary microbiota for detecting periodontitis.

Saliva contains diverse bacteria shed from various oral sites, including subgingival plaque. It is reasonable to focus on the total occupancy of subgingival plaque-specific bacteria (SUBP bacteria), which live in subgingival environments, in the saliva for detecting periodontitis using salivary testing. This study aimed to validate the clinical utility of SUBP bacteria in the salivary microbiota for the detection of periodontitis. We examined stimulated saliva samples collected from 125 subjects who visited three dental clinics. The relative abundances of previously identified 11 SUBP bacteria were determined using 16S ribosomal RNA gene sequencing and a reference-based approach. The prediction performance was evaluated using a receiver operating characteristic (ROC) curve. The SUBP bacteria accounted for 0-15.4% of the salivary microbiota, and the percentage distinguished periodontitis patients with at least 15 sites with probing depth ≥4 mm with a sensitivity of 0.90 (95% confidence interval [CI], 0.81-0.98) and specificity of 0.70 (95% CI, 0.60-0.80) (area under the ROC curve [AUC], 0.87). Among 2,047 combinations of 11 SUBP bacteria, combinations including Streptococcus constellatus, Porphyromonas gingivalis, and Fusobacterium nucleatum subsp. vincentii demonstrated significantly higher AUC values in their detection. These results suggest that examining SUBP bacteria in saliva may be useful for detecting periodontitis patients in mass screening.

Airflow limitation and tongue microbiota in community-dwelling elderly individuals.

Numerous oral indigenous microorganisms are constantly introduced into the stomach via the laryngopharynx, and a portion of these microorganisms irregularly reaches the lower airways and lungs. This study investigated the association between airflow limitation and the status of tongue microbiota, which is a primary source of ingested oral bacterial populations. The study population consisted of 484 community-dwelling adults aged 70-80 years inhabiting Hisayama town, Japan, who underwent a regular health examination including dental examination and spirometry test in 2016. The bacterial density and composition of their tongue microbiota were determined using a previously used 16S rRNA gene to understand their relationship with oral health conditions. The present cross-sectional study compared the tongue microbiota status between elderly individuals with airflow limitation and those with normal airflow. The total bacterial density of the tongue microbiota of individuals with airflow limitation was significantly higher than that of individuals with normal airflow. Logistic regression analysis demonstrated that a high-biomass tongue microbiota was significantly associated with airflow limitation after adjustment for smoking intensity and other covariates (adjusted OR 1.61, 95% CI 1.01-2.60). Of the predominant commensals, higher amounts of Prevotella melaninogenica and Actinomyces odontolyticus were associated with a higher prevalence of airflow limitation. These results indicate that increased bacterial burden in the tongue microbiota is associated with a higher prevalence of airflow limitation.

Tongue Microbiota Composition and Dental Caries Experience in Primary School Children.

The tongue microbiota of elderly adults is composed of two cohabiting commensal groups and their ratios are related to the number of teeth with dental caries experience. In this study, the variation in the tongue microbiota of primary school children and its relationship with the dental caries experience were investigated. We examined the tongue microbiota of 138 children aged 6 to 7 years and 11 to 12 years (61 and 77 children, respectively) who underwent annual dental examinations. The bacterial composition was determined by sequencing the V1-V2 region of the 16S rRNA gene. Cooccurrence network analysis indicated two groups of cohabiting predominant commensals in the tongue microbiota of children. The microbiota in children without a history of dental caries showed significantly higher relative abundances of one of the cohabiting groups, primarily composed of Neisseria subflava, Porphyromonas pasteri, and Fusobacterium periodonticum, compared to that in children with a history of dental caries, which is consistent with that of elderly adults with fewer teeth with dental caries experience. Linear discriminant analysis effect size (LEfSe) further identified Streptococcus oralis subsp. dentisani, belonging to the aforementioned commensal group, as a discriminant species in children without dental caries experience aged 6 to 7 years and 11 to 12 years. Our results describe the tongue microbiota composition of primary school children without history of dental caries and support the possibility that dental caries experience is accompanied by a shift in the tongue microbiota.IMPORTANCE Dental caries is now considered to be caused by acids produced by the overall dental plaque microbiota rather than by specific pathogens. This study focused on the relationship between dental caries experience and the variations in tongue microbiota, which is adjacent but separate from the dental plaque microbiota. Our results demonstrated that the tongue microbiota of primary school children with no history of dental caries experience was composed of predominant commensals with different relative abundances compared to those present in children with dental caries experience, suggesting that dental caries experience is accompanied by a shift in the tongue microbiota. The maintenance of a healthy tongue microbiota may indirectly contribute to the prevention of dental caries.

Compositional Shift of Oral Microbiota Following Surgical Resection of Tongue Cancer.

Salivary microbiota is considered a source of microorganisms for the respiratory and digestive tracts, and a trigger for diseases in these distant organs. Meanwhile, the microbiota on the tongue surface is thought to be a major source of salivary microbiota. Therefore, surgical resection of the tongue for definitive treatment of oral cancer could drastically change the salivary bacterial balance and virulence. Here, we investigated the shift of the salivary microbiota following surgical resection in patients with tongue cancer. The stimulated saliva samples were collected from 25 tongue cancer patients pre- and post-resection of the tongue, and bacterial density and composition was determined using quantitative PCR analysis and 16S ribosomal RNA (rRNA) gene sequencing, respectively. Although no significant difference in the total bacterial density in saliva pre- and post-surgery was observed, the bacterial composition significantly differed according to the analysis of similarity. Among predominant operational taxonomic units (OTUs) with ≥1% of relative abundance, the proportions of OTUs corresponding to Streptococcus salivarius, Prevotellamelaninogenica, and Prevotellahisticola were significantly decreased following the tongue resection. On the other hand, the proportions of OTUs corresponding to Lautropiamirabilis, Neisseriaflava, Streptococcussanguinis, and Fusobacterium nucleatum, known to be inhabitants of dental plaque, were significantly increased. These results suggest that surgical resection of the tongue causes a compositional shift of the salivary microbiota, characterized by an increase in bacterial species derived from dental plaque, including periodontal pathogens. These results suggest the necessity of more careful and frequent postoperative oral care after surgical resection of tongue cancer.

Disrupted tongue microbiota and detection of nonindigenous bacteria on the day of allogeneic hematopoietic stem cell transplantation.

Disruption of the intestinal microbiota caused by intensive chemotherapy, irradiation and antibiotics can result in development of severe gut graft-versus-host disease and infectious complications, leading to poorer outcomes among allogeneic hematopoietic stem cell transplantation (allo-HSCT) recipients. Although the oral cavity is also densely colonized by indigenous microorganisms, the bacterial composition in allo-HSCT recipients remains unclear. We determined the tongue microbiota composition of 45 patients with hematological disorders on the day of transplantation and compared them to 164 community-dwelling adults. The V1-V2 regions of the 16S rRNA gene sequences demonstrated that the allo-HSCT recipients had less diverse and distinct microbiota from that of community-dwelling adults. The full-length 16S rRNA gene sequences identified 146 bacterial taxa in the microbiota of allo-HSCT recipients, of which 34 bacterial taxa did not correspond to bacteria primarily inhabiting the oral cavity deposited in the expanded Human Oral Microbiome Database. Notably, the detection of Staphylococcus haemolyticus and/or Ralstonia pickettii was significantly associated with a higher risk of mortality during the follow-up period. These results demonstrate that the oral cavity of allo-HSCT recipients is colonized by a disrupted microbiota on the day of transplantation and suggest that detection of specific nonindigenous taxa could be a predictor of transplant outcome.

Identification of Initial Colonizing Bacteria in Dental Plaques from Young Adults Using Full-Length 16S rRNA Gene Sequencing.

Development of dental plaque begins with the adhesion of salivary bacteria to the acquired pellicle covering the tooth surface. In this study, we collected in vivo dental plaque formed on hydroxyapatite disks for 6 h from 74 young adults and identified initial colonizing taxa based on full-length 16S rRNA gene sequences. A long-read, single-molecule sequencer, PacBio Sequel, provided 100,109 high-quality full-length 16S rRNA gene sequence reads from the early plaque microbiota, which were assigned to 90 oral bacterial taxa. The microbiota obtained from every individual mostly comprised the 21 predominant taxa with the maximum relative abundance of over 10% (95.8 ± 6.2%, mean ± SD), which included Streptococcus species as well as nonstreptococcal species. A hierarchical cluster analysis of their relative abundance distribution suggested three major patterns of microbiota compositions: a Streptococcus mitis/Streptococcus sp. HMT-423-dominant profile, a Neisseria sicca/Neisseria flava/Neisseria mucosa-dominant profile, and a complex profile with high diversity. No notable variations in the community structures were associated with the dental caries status, although the total bacterial amounts were larger in the subjects with a high number of caries-experienced teeth (≥8) than in those with no or a low number of caries-experienced teeth. Our results revealed the bacterial taxa primarily involved in early plaque formation on hydroxyapatite disks in young adults.IMPORTANCE Selective attachment of salivary bacteria to the tooth surface is an initial and repetitive phase in dental plaque development. We employed full-length 16S rRNA gene sequence analysis with a high taxonomic resolution using a third-generation sequencer, PacBio Sequel, to determine the bacterial composition during early plaque formation in 74 young adults accurately and in detail. The results revealed 21 bacterial taxa primarily involved in early plaque formation on hydroxyapatite disks in young adults, which include several streptococcal species as well as nonstreptococcal species, such as Neisseria sicca/N flava/N mucosa and Rothia dentocariosa Given that no notable variations in the microbiota composition were associated with the dental caries status, the maturation process, rather than the specific bacterial species that are the initial colonizers, is likely to play an important role in the development of dysbiotic microbiota associated with dental caries.

Effect of coffee on the compositional shift of oral indigenous microbiota cultured in vitro.

Coffee is a widely consumed beverage containing organic compounds with antibacterial activity. To investigate its possible effect on the growth of oral indigenous microbiota, saliva samples collected from nine young adults were inoculated into brain heart infusion (BHI) medium with or without addition of coffee compounds and cultured at 37°C in 5% CO2 for 12 h. The total bacterial density and composition after cultivation for 0, 6, and 12 h were determined by quantitative PCR analysis and 16S rRNA gene sequencing, respectively. The increase in total bacterial load was significantly inhibited by addition of the coffee compounds. The microbiota was mostly composed of Streptococcus species after culture in BHI medium regardless of the addition of coffee compounds. The proportion of Streptococcus salivarius was significantly reduced after addition of coffee relative to that in untreated medium alone, whereas the proportions of Streptococcus mitis and Streptococcus infantis were increased. These results suggest that exposure to coffee affects the composition of the oral Streptococcus population, in addition to inhibiting the overall growth of salivary bacteria. Considered in the light of data from earlier epidemiological studies, it is possible to conclude that coffee consumption contributes to better health.

Characteristics of the Salivary Microbiota in Patients With Various Digestive Tract Cancers.

The salivary microbiota is constantly swallowed and delivered to the digestive tract. These bacteria may be associated with gastrointestinal diseases. This case-control study examined the salivary microbiota in patients with digestive tract cancer (DTC) and evaluated their differential distribution based on the cancer sites. We collected saliva samples from 59 patients with cancer in any part of the digestive tract (tongue/pharynx, esophagus, stomach, and large intestine) and from 118 age- and sex-matched control subjects. There was no significant difference in periodontal status between DTC patients and control subjects (P = 0.72). We examined the bacterial diversity and composition in saliva by 16S ribosomal RNA gene sequencing. Salivary bacterial diversity in DTC patients was significantly higher than that in control subjects [number of operational taxonomic units (OTUs), P = 0.02; Shannon index, P < 0.01; Chao1, P = 0.04]. Eleven differentially abundant OTUs in DTC patients were identified using the linear discriminant analysis effect size (LEfSe) method. Based on the cancer sites, the diversity of salivary bacteria was especially higher in tongue/pharyngeal or esophageal cancer patients than in control subjects. Among the 11 differentially abundant OTUs in DTC patients, an OTU corresponding to Porphyromonas gingivalis was more abundant in the saliva of all groups of DTC patients compared to that in control subjects, and an OTU corresponding to Corynebacterium species was more abundant in all groups other than gastric cancer patients (P < 0.01). In addition, the relative abundances of OTUs corresponding to Fusobacterium nucleatum, Streptococcus parasanguinis II, and Neisseria species were significantly higher in tongue/pharyngeal cancer patients compared to their abundances in control subjects (P < 0.01). The relative abundance of an OTU corresponding to the Neisseria species was also significantly higher in gastric cancer patients and that of an OTU corresponding to Actinomyces odontolyticus was significantly higher in colorectal cancer patients (P < 0.01). These results suggest that the salivary microbiota might be associated with various digestive tract cancers.

Transition of Bacterial Diversity and Composition in Tongue Microbiota during the First Two Years of Life.

Newborns are constantly exposed to various microbes from birth; hence, diverse commensal bacteria colonize the oral cavity. However, how or when these bacteria construct a complex and stable ecosystem remains unclear. This prospective cohort study examined the temporal changes in bacterial diversity and composition in tongue microbiota during infancy. We longitudinally collected a total of 464 tongue swab samples from 8 infants (age of <6 months at baseline) for approximately 2 years. We also collected samples from 32 children (aged 0 to 2 years) and 73 adults (aged 20 to 29 years) cross-sectionally as control groups. Bacterial diversities and compositions were determined by 16S rRNA gene sequencing. The tongue bacterial diversity in infancy, measured as the number of observed operational taxonomic units (OTUs), rapidly increased and nearly reached the same level as that in adults by around 80 weeks. The overall tongue bacterial composition in the transitional phase, 80 to 120 weeks, was more similar to that of adults than to that of the early exponential phase (EEP), 10 to 29 weeks, according to analysis of similarities. Dominant OTUs in the EEP corresponding to Streptococcus peroris and Streptococcus lactarius exponentially decreased immediately after EEP, around 30 to 49 weeks, whereas several OTUs corresponding to Granulicatella adiacens, Actinomyces odontolyticus, and Fusobacterium periodonticum reciprocally increased during the same period. These results suggest that a drastic compositional shift of tongue microbiota occurs before the age of 1 year, and then bacterial diversity and overall bacterial composition reach levels comparable to those in adults by the age of 2 years.IMPORTANCE Evaluating the development of oral microbiota during infancy is important for understanding the subsequent colonization of bacterial species and the process of formation of mature microbiota in the oral cavity. We examined tongue microbiota longitudinally collected from 8 infants and found that drastic compositional shifts in tongue microbiota occur before the age of 1 year, and then bacterial diversity and overall bacterial composition reach levels comparable to those in adults by the age of 2 years. These results may be helpful for preventing the development of various diseases associated with oral microbiota throughout life.

Denture Wearing Moderates the Association between Aspiration Risk and Incident Pneumonia in Older Nursing Home Residents: A Prospective Cohort Study.

Aspiration is increasingly recognized as a major risk for pneumonia, but a potential link between wearing dentures and incident pneumonia with aspiration risk is unclear. The aim of this study was to investigate whether denture wearing moderates the association between aspiration risk and incident pneumonia in older adults. We used prospective cohort data of 156 residents aged >70 years from eight nursing homes in Aso, Japan. Aspiration risk was evaluated using the modified water swallowing test. During a 1-year follow-up (2014 to 2015), information on incident pneumonia was obtained from nursing home medical records. During follow-up, pneumonia developed in 7.1% of participants. In the multivariate-adjusted Cox proportional hazards model, after adjusting for potential confounders, aspiration risk was independently associated with a 4.4-fold higher hazard ratio (HR) of incident pneumonia (95% confidence interval, CI, 1.16⁻16.43). The difference in the risk of incident pneumonia between subjects with aspiration risk who were wearing dentures and those not at risk of aspiration was not significant, whereas those with aspiration risk without dentures had a 7.3-fold higher HR of incident pneumonia than those not at risk of aspiration (95% CI, 1.02⁻52.63). Denture wearing might partially moderate the increased risk of incident pneumonia associated with aspiration risk.

Tongue Microbiota and Oral Health Status in Community-Dwelling Elderly Adults.

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.