Smoking displays the greatest impact on periodontitis among lifestyle-related factors. Both smoking and obesity are independent risk indicators for periodontitis; moreover, these parameters exhibit a dose-response relationship with respect to periodontitis risk.

The FimA fimbriae of Porphyromonas gingivalis, the causative agent of periodontitis, have been implicated in various aspects of pathogenicity, such as colonization, adhesion and aggregation. In this study, the four open reading frames (ORF1, ORF2, ORF3 and ORF4) downstream of the fimbrilin gene (fimA) in strain ATCC 33277 were examined. ORF2, ORF3 and ORF4 were demonstrated to encode minor components of the fimbriae and were therefore renamed fimC, fimD and fimE, respectively. Immunoblotting analyses revealed that inactivation of either fimC or fimD by an ermF-ermAM insertion, but not inactivation of ORF1, was accompanied by concomitant loss of the products from the downstream genes, raising the possibility that fimC, fimD and fimE constitute a transcription unit. The fimE mutant produced FimC and FimD, but fimbriae purified from it contained neither protein, suggesting that FimE is required for the assembly of FimC and FimD onto the fimbrilin (FimA) fibre. The fimC, fimD and fimE mutants lost autoaggregation abilities. Fimbriae purified from these three mutants showed attenuated binding activities to glyceraldehyde-3-phosphate dehydrogenase of Streptococcus oralis and to two extracellular matrix proteins, fibronectin and type I collagen. These results suggest that FimE, as well as FimC and FimD, play critical roles in the adhesive activities of the mature FimA fimbriae in P. gingivalis.

Cohesive interactions between Porphyromonas gingivalis and plaque-forming bacteria, such as Streptococcus oralis, are considered to play an important role in the colonization of P. gingivalis in periodontal sites. Although P. gingivalis fimbriae have been reported to mediate coaggregation with S. oralis, the S. oralis molecule involved has not been identified. We identified the coadhesin of S. oralis ATCC 9811 and purified it by affinity column chromatography. We found that the molecular mass of the purified protein was approximately 40 kDa. Dot blot and Western blot assays showed binding of the 40-kDa protein to P. gingivalis fimbriae. Further, turbidimetric assays showed that the coadhesin inhibited coaggregation between P. gingivalis and S. oralis in a dose-dependent manner. Analyses of the amino-terminal sequences of the protein and its lysyl endopeptidase-cleaved fragments revealed that the coadhesin was identical to glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Next, we cloned the gene that encodes S. oralis GAPDH and found that the sequence had a high degree of homology with the sequences of GAPDHs of various bacteria, including Streptococcus gordonii and Fusobacterium nucleatum. To confirm the contribution of S. oralis GAPDH to the interaction with P. gingivalis, a recombinant GAPDH protein was generated in Escherichia coli; this protein bound to P. gingivalis fimbriae and had an inhibitory effect on coaggregation. These results suggest that S. oralis GAPDH functions as a coadhesin for P. gingivalis fimbriae. In addition, considering the high degree of homology of the GAPDHs of various bacteria, those of other plaque-forming bacteria also may contribute to the colonization of P. gingivalis.Porphyromonas gingivalis is considered to be a prominent periodontopathogen, as it possesses a variety of virulence factors, such as proteinases, hemagglutinin, and lipopolysaccharide (28,37,41). In order to cause infection, it is necessary for P. gingivalis to attach to tooth surfaces, subgingival epithelium, or early colonizing gram-positive bacteria; this step constitutes the initial stage of colonization in periodontal pockets (38). In addition, the bacterium has been reported to interact with a variety of other oral gram-positive bacteria (19), including Actinomyces naeslundii (36, 43), Actinomyces viscosus (9, 12, 26, 27, 36), Streptococcus gordonii (23), Streptococcus mutans (17), Streptococcus oralis (29), and Streptococcus sanguis (39); these interactions are considered to play a vital role in the colonization of P. gingivalis in the oral cavity.P. gingivalis possesses several cell surface components that are important for its attachment. Its fimbriae have been shown to interact with epithelial cells (15), cultured human fibroblasts (20), and saliva-coated hydroxyapatite beads (2, 32), while its vesicles have been shown to interact with collagen-coated hydroxyapatite beads (32). Further, in studies to determine which of the surface components of P. gingivalis interact with grampositive bacteria, its fimbri...

Smoking exerted the greatest influence on periodontitis risk among lifestyle factors. Smoking may suppress the host-defense system, which may promote periodontal disease progression.

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