INTRODUCTION: Tannerella forsythia (Tf) is one of the periodontal organisms recently implicated in the development of periodontal diseases. Studies from our laboratories have shown that the Tf BspA protein, a bacterial surface protein belonging to the leucine-rich repeat protein family, is involved in coaggregation with Fusobacterium nucleatum (Fn) and induces proinflammatory cytokines from monocytes. Therefore, the BspA protein may represent an important virulence factor of Tf. The contact stimulus encountered when bacteria attach to its site of infection or biofilms is an important external signal that has been proposed to regulate expression of virulence factors and this contact dependent regulation may have specific roles in pathogenesis. OBJECTIVE: The present study was carried out to determine if BspA is regulated in a contact-dependent manner. METHODS: Levels of BspA transcripts were determined by real-time PCR using a fluorescent-labeled BspA-specific probe and appropriately designed primers with: i) planktonic cells, ii) biofilm cells on plastic surfaces, iii) mixed biofilms of Tf with Fn, and iv) in the presence of Porphyromonas gingivalis vesicles. RESULTS: Our results showed that the expression of BspA is down regulated up to three-fold in both Tf biofilms and mixed Fn/Tf synergistic biofilms as compared to planktonic cells. Further, Pg vesicles promoted aggregation of Tf cells and also enhanced biofilm formation by Tf. The expression of BspA was down-regulated under these conditions compared to Tf cells in the absence of vesicles. CONCLUSIONS: Our results showed that the expression of BspA is significantly reduced as a result of contact stimulus. This contact-dependent down-regulation of BspA may be a bacterial mechanism for evading host immune responses following attachment and during biofilm growth. Studies are in progress to study the mechanism of this contact dependent inhibition. This study was supported by NIDCR grant DE 014749

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