Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2019

Polymicrobial Nature of Chronic Oral Disease (#193)

Stuart Dashper 1
  1. University of Melbourne, Parkville, VIC, Australia

Polymicrobial biofilms are complex, dynamic microbial communities that are important for the persistence and proliferation of participating microbes in the environment. Some chronic human diseases are caused by dysbioses in these communities that usually result in reduced diversity and a community dominated by a group of specific pathobionts. In the human oral cavity dysbiosis in subgingival plaque communities can lead to an increased abundance of specific anaerobic pathobionts, including the highly proteolytic, sessile Porphyromonas gingivalis and the motile spirochaete, Treponema denticola. In vivo, increases in T. denticola and P. gingivalis abundance are predictive of chronic periodontal disease progression. P. gingivalis and T. denticola co-exist in deep periodontal pockets and have been co-localized to the superficial layers of subgingival plaque as microcolony blooms adjacent to the epithelial cell layer, where they benefit from a dysregulated host inflammatory response. P. gingivalis and T. denticola specifically adhere to each other and decorate each other with outer membrane vesicles. P. gingivalis and T. denticola exhibit synergistic pathogenicity in animal models of disease, synergistic biofilm formation and development, and display a symbiotic relationship in nutrient utilization and growth promotion. Co-culture causes significant changes in global gene expression in both species, with T. denticola genes encoding virulence factors and glycine catabolic pathways being significantly up-regulated. T. denticola utilises glycine as a major energy and carbon source whilst in monoculture P. gingivalis produces excess free glycine. Free glycine release by P. gingivalis is stimulated by T. denticola which is due to the collaborative hydrolysis of peptides by proteases of both species. These processes enable these species to partition their environment and avoid competition for nutrients. T. denticola motility although not usually considered as a classic virulence factor, is involved in synergistic biofilm development between P. gingivalis and T. denticola. Collectively these data suggest an intimate relationship between these two species that has evolved to enhance their survival and virulence.