The secretion of certain proteins in Porphyromonas gingivalis is dependent on a C-terminal domain (CTD). After secretion, the CTD is cleaved prior to extensive modification of the mature protein, probably with lipopolysaccharide, therefore enabling attachment to the cell surface. In this study, bioinformatic analyses of the CTD demonstrated the presence of three conserved sequence motifs. These motifs were used to construct Hidden Markov Models (HMMs) that predicted 663 CTD-containing proteins in 21 fully sequenced species of the Bacteroidetes phylum, while no CTD-containing proteins were predicted in species outside this phylum. Further HMM searching of Cytophaga hutchinsonii led to a total of 171 predicted CTD proteins in that organism alone. Proteomic analyses of membrane fractions and culture fluid derived from P. gingivalis and four other species containing predicted CTDs (Parabacteroides distasonis, Prevotella intermedia, Tannerella forsythia, and C. hutchinsonii) demonstrated that membrane localization, extensive post-translational modification, and CTD-cleavage were conserved features of the secretion system. The CTD cleavage site of 10 different proteins from 3 different species was determined and found to be similar to the cleavage site previously determined in P. gingivalis, suggesting that homologues of the C-terminal signal peptidase (PG0026) are responsible for the cleavage in these species.

Monitoring the proportions of P. gingivalis and T. denticola in subgingival plaque has the potential to help identify sites at significant risk for progression of periodontitis, which would assist in the targeted treatment of disease.

Remineralisation has been shown to be an effective mechanism of preventing the progression of enamel caries. The aim of this double-blind, randomised, cross-over in situ study was to compare enamel remineralisation by chewing sugar-free gum with or without casein phosphopeptide amorphous calcium phosphate (CPP-ACP) where the enamel lesions were exposed to dietary intake and some were covered with gauze to promote plaque formation. Participants wore removable palatal appliances containing 3 recessed enamel half-slabs with subsurface lesions covered with gauze and 3 without gauze. Mineral content was measured by transverse microradiography, and plaque composition was analysed by real-time polymerase chain reaction. For both the gauze-free and gauze-covered lesions, the greatest amount of remineralisation was produced by the CPP-ACP sugar-free gum, followed by the gum without CPP-ACP and then the no-gum control. Recessing the enamel in the appliance allowed plaque accumulation without the need for gauze. There was a trend of less remineralisation and greater variation in mineral content for the gauze-covered lesions. The cell numbers of total bacteria and streptococci were slightly higher in the plaque from the gauze-covered enamel for 2 of the 3 treatment legs; however, there was no significant difference in Streptococcus mutans cell numbers. In conclusion, chewing sugar-free gum containing CPP-ACP promoted greater levels of remineralisation than a sugar-free gum without CPP-ACP or a no-gum control using an in situ remineralisation model including dietary intake irrespective of whether gauze was used to promote plaque formation or not.

Background Human microbiomes assemble in an ordered, reproducible manner yet there is limited information about early colonisation and development of bacterial communities that constitute the oral microbiome. Aim The aim of this study was to determine the effect of exposure to breastmilk on assembly of the infant oral microbiome during the first 20 months of life. Methods The oral microbiomes of 39 infants, 13 who were never breastfed and 26 who were breastfed for more than 10 months, from the longitudinal VicGeneration birth cohort study, were determined at four ages. In total, 519 bacterial taxa were identified and quantified in saliva by sequencing the V4 region of the bacterial 16S rRNA genes. Results There were significant differences in the development of the oral microbiomes of never breastfed and breastfed infants. Bacterial diversity was significantly higher in never breastfed infants at 2 months, due largely to an increased abundance of Veillonella and species from the Bacteroidetes phylum compared with breastfed infants. Conclusion These differences likely reflect breastmilk playing a prebiotic role in selection of early-colonising, health-associated oral bacteria, such as the Streptococcus mitis group. The microbiomes of both groups became more heterogenous following the introduction of solid foods.

Aim Periodontitis is a site-specific, chronic disease treated by non-surgical debridement of subgingival plaque. We aimed to determine the microbiome of sites that did not respond to this treatment (NR) compared with paired good responding (GR) sites before and after treatment. Materials and methods In a longitudinal cohort study, clinical parameters of disease and biological samples were taken prior to and 3 months after treatment. Twelve NR sites from six participants were paired with GR sites within the same participant. Subgingival plaque samples were subjected to bacterial community analysis using 16S rRNA gene sequencing. Results There were no significant differences in clinical parameters and microbial communities at baseline between GR and NR sites. Bacterial communities in deep pockets were dominated by a small number of species, notably Porphyromonas gingivalis and Treponema denticola . In NR sites three months after treatment there was no significant change in bacterial composition whilst there was a collapse in the abundance of pathobionts in GR sites. Conclusion NR sites were not identifiable prior to treatment by clinical or microbiological parameters. Treatment failed to disrupt pathogenic bacterial community in NR sites. Targeted suppression of particular species should be considered to initiate community collapse and aid disease resolution.