Role of coaggregation among periodontopathic bacteria in formation of periodontopathic biofilm

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Objects : Periodontitis is caused by Gram-negative rods and spirochetes. Porphyromonas gingivalis is a major pathogen of chronic periodontal disease, This microorganism has a number of virulence factors, including fimbriae, lipopolysaccharides and proteases, and is often co-isolated with Tannerella forsythensis and Treponema denticola. The combination of these three microorganisms is known as the "red complex", and is thought to play an important role in the progression of chronic periodontitis. In this project, we investigated coaggregation and synergistic effects among these periodontopathic bacteria to clarify the underlying mechanisms of periodontopathic biofilm formation.Materials and Methods : Coaggregation between P.gingivalis ATCC 33277 and T.denticola ATCC 35405 was evaluated by absorbance at 660 nm in coaggregation buffer. To clarify which P.gingivalis ligands were involved in coaggregation, knockout mutants lacking gingipains and fimbriae were constructed. Synergistic effect … More s on biofilm formation were evaluated by using a two-compartment co-culture system incorporating a 0.4 m filter unit.Results and Discussion : Coaggregation reaction between P.gingivalis and T.denticola was decreased in the Mfa1 deficient mutant, kgp, RgpA and RgpB deficient mutant and Kgp, RgpA and HagA deficient mutant. These results indicated that gingipains and Mfa1 were involved in the coaggregation reaction. In particular, activity decreased significantly in the Kgp, RgpA and RgpB deficient strain and Kgp, RgpA and HagA deficient strain. In addition, coaggregation activity was observed in the Mfa1 FimA mutant. This suggests that the hemagglutinin/ahesion domains of gingipains and HagA play a key role in the coaggregation reaction. Using our two-compartment system, Fusobacterium nucleatum showed an approximately four-fold increase in biofilm formation in co-culture with P.gingivalis compared with that obtained with single culture alone. Taken together, these results suggest that the coaggregation reaction of P.gingivalis with other periodontopathogens is involved not only in the colonization of gingival crevicular biofilms, but also in the formation of periodontopathic biofilms. Less