The oral cavity contains a variety of ecological niches with very different environmental conditions that shape biofilm structure and composition. The space between the periodontal tissue and the tooth surface supports a unique anaerobic microenvironment that is bathed in the nutrient-rich gingival crevicular fluid (GCF). During the development of periodontitis, this environment changes and clinical findings reported a sustained level of calcium ion concentration in the GCF collected from the periodontal pockets of periodontitis patients. Here, we report the effect of calcium ion supplementation on human oral microbial biofilm formation and community composition employing an established SHI medium-based in vitro model system. Saliva-derived human microbial biofilms cultured in calcium-supplemented SHI medium (SHICa) exhibited a significant dose-dependent increase in biomass and metabolic activity. The effect of SHICa medium on the microbial community composition was evaluated by 16S rRNA gene sequencing using saliva-derived microbial biofilms from healthy donors and periodontitis subjects. In this study, intracellular microbial genomic DNA (iDNA) and extracellular DNA (eDNA) were analyzed separately at the genus level. Calcium supplementation of SHI medium had a differential impact on iDNA and eDNA in the biofilms derived from healthy individuals compared to those from periodontitis subjects. In particular, the genus-level composition of the eDNA portion was distinct between the different biofilms. This study demonstrated the effect of calcium in a unique microenvironment on oral microbial complex supporting the dynamic transformation and biofilm formation.

RadD, a major adhesin of oral fusobacteria, is part of a four-gene operon encoding the small lipoprotein FAD-I and two currently uncharacterized small proteins encoded by the rapA and rapB genes. Previously, we described a role for FAD-I in the induction of human B-defensin 2 (hBD2) upon contact with oral epithelial cells. Here, we investigated potential roles for fad-I, rapA, and rapB in interspecies interaction and biofilm formation. Gene inactivation mutants were generated for each of these genes in the nucleatum and polymorphum subspecies of Fusobacterium nucleatum and characterized for their adherence to partner species, biofilm formation, and operon transcription. Binding to Streptococcus gordonii was increased in all mutant strains with Δfad-I having the most significant effect. This increased adherence was directly proportional to elevated radD transcript levels and resulted in significantly different architecture and height of the biofilms formed by Δfad-I and S. gordonii compared to the wild-type parent. In conclusion, FAD-I is important for fusobacterial interspecies interaction as its lack leads to increased production of the RadD adhesin suggesting a role of FAD-I in its regulation. This regulatory effect does not require the presence of functional RadD.

Background: This study investigated the microbial changes during treatment with clear aligners (CA) and fixed appliances (FA) and evaluated the utility of saliva as a diagnostic marker in orthodontic patients. Methods: Ten patients each were enrolled in the FA and CA groups. Plaque (PI) and gingival indices (GI) were measured at baseline, three, six and 12 months. Saliva and plaque samples were collected at each time point for determination of the respective microbial community composition via 16S rRNA sequencing. Results: PI and GI increased significantly over time only in FA patients. While alpha diversity was similar for FA or CA patients, beta diversity and microbial community composition analysis revealed significant differences between saliva and plaque for both treatment groups. Further analysis of the relative abundance of certain health- and disease-associated genera present in the saliva and plaque of FA and CA patients correlated with the clinical parameters. Conclusions: Clinical parameters significantly worsened during orthodontic treatment with FA but not CA. The microbial composition of plaque and saliva differed significantly between treatment groups. However, the changes in abundance of some individual genera were similar in both saliva and plaque in correlation with the corresponding clinical parameters. These genera show potential as biomarkers for health and disease. Practical implications: Monitoring of the microbial community composition during orthodontic treatment could reduce the risk of oral disease development. While the microbial composition of saliva is not reflective of the plaque communities implicated in oral health and disease, individual marker genera show promise as biomarkers.

Denture stomatitis (DS) is a common infection in denture wearers, especially women. This study evaluated the induction of DS using acrylic devices attached to the palate of rats combined with inoculation of Candida spp. Immunocompetent male and female rats received a carbohydrate-rich diet. Impressions were taken from the rats’ palate to individually fabricate acrylic devices. Mono- and multispecies biofilms of C. albicans, C. glabrata, and C. tropicalis were grown on the devices, which were then cemented on posterior teeth and kept in the rats’ palate for four weeks. Microbial samples from the palate and the device were quantified. Oral microbiome of rats inoculated with C. albicans was analyzed by 16S rRNA gene sequencing. Log₁₀(CFU/mL) were analyzed by mixed or two-way MANOVA (α = 0.05). Candida spp. and acrylic device did not induce palatal inflammation macroscopically nor microscopically. Although there was an increase (p < 0.001) of the total microbiota and female rats demonstrated higher (p = 0.007) recovery of Candida spp. from the palate, the gender differences were not biologically relevant. The microbiome results indicate an increase in inflammatory microbiota and reduction in health-associated micro-organisms. Although Candida spp. and acrylic device did not induce DS in immunocompetent rats, the shift in microbiota may precede manifestation of inflammation.

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In this study, a mutant library was screened to identify the Streptococcus sanguinis proteins involved in binding to Fusobacterium nucleatum during biofilm formation. Seven mutants showed a significant defect in the interaction with F. nucleatum, and the affected genes encoded the adhesins SspD and CrpA, three proteins with pleiotropic function (YidC, SrtB and DltB), a predicted stomatin/prohibitin-like membrane protease subunit and a hypothetical protein. These proteins could serve as therapeutic targets to prevent biofilm-related oral diseases.