Environmental effects on oral biofilm communities

Background: Periodontitis is associated with shifts in the balance of the microbial composition of subgingival biofilms. Many species that predominate in disease have not been isolated from healthy sites or are found in low abundance, raising questions as to the reservoir or origin of these putative pathogens. Aims: This project aims to generate an in vitro model of dysbiosis to demonstrate whether it is possible to observe the outgrowth of low abundance disease-associated species from biofilms taken from healthy sites and subjects by mimicking a disease-promoting environment. Materials and Methods: The Calgary Biofilm Device and several types of protein-rich media were used to culture five-species microbial communities. Then, the optimised model was used to culture complex biofilms using an inoculum of plaque and saliva from healthy young adult volunteers in media mimicking the nutritional status of the inflamed periodontal pocket. Later, three-week complex biofilms were cultured just in sterile human saliva to see whether changes in the enriched biofilms could be reversed. Metagenomics was used to characterise the taxonomy and functional potential of biofilms, and longitudinal comparisons were performed on biofilms and the inoculum. Results: The inoculum consisted mainly of health-associated genera, such as Streptococcus, Actinomyces and Haemophilus. After culture in various media for one or three weeks, the biofilm composition shifted and numerous fastidious and periodontal disease-associated species belonging to genera Bacteroidetes, Fretibacterium, Prevotella and Alloprevotella were enriched. These enriched biofilms, subsequently cultured solely in human saliva, showed a minor decrease in disease associated-species. There was a shift in functional activities, with cultured biofilms having a greater abundance of genes associated with virulence. Conclusion: The results suggest that the source of the periodontal pathogens is the healthy human mouth, and that these species can be enriched at the expense of health-associated species in a nutritional environment resembling inflammation.