Coaggregation Modulates Alveolar Bone Loss in Mixed Infection with P.gingivalis&F.nucleatum

Background: Porphyromonas gingivalis and Fusobacterium nucleatum are among the main pathogens in the initiation and progression of periodontal diseases. The two bacteria are also linked to each other by co-aggregation, which is inhibitable by lactose. It was shown that P. gingivalis induces alveolar bone loss in mice after oral bacterial challenge in mice. The effect of the co-aggregation between the two bacteria on the alveolar bone loss has not been characterized. Objectives: The present study was designed to investigate the bone loss induced by mixed infection of P. gingivalis and F. nucleatum, and to characterize the role of co-aggregation between the two bacteria on the observed response. Methods: After 10 days of antibiotic treatment and 3 days of wash-out, mice were challenged orally 3 times in 2 days intervals with an innoculum of P. gingivalis, F. nucleatum or a mixture of the two. Six weeks later, the jaws were harvested and the alveolar bone volume was measured using micro-CT. Inhibition of co-aggregation was induced using lactose. Results: Oral mono-infection with P. gingivalis or F. nucleatum did not induce significant bone loss compared to that of the controls. However, the same concentration challenge of mixed infection induced significant bone loss conpared to the mono-infected and control groups. Prevention of bacterial aggregation in the mixed infection group augmented the bone loss. Conclusions: Mixed infection with P. gingivalis and F. nucleatum enhanced alveolar bone loss compared to mono-infection with either bacterium. The finding that Inhibition of aggregation augmented the bone loss suggests that aggregation between P. gingivalis and F. nucleatum may reduce the virulence of the infection.