Molecular and Immunological Characterization of the Fimbriae of Porphyromonas gingivalis

Shigeyuki Hamada*, Taku Fujiwara, Seiji Morishima, Ichiro Takahashi, Ichiro Nakagawa, Shigenobu Kimura, and Tomohiko Ogawa Department of Oral Microbiology, Osaka University Faculty of Dentistry, Suita, Osaka 565, Japan Received September 12, 1994 Key words: Porphyromonas gingivalis, Fimbriae, fimA gene, Synthetic peptide, Periodontitis1. Introduction A wide variety of bacteria including Gram-posi-tive and Gram-negative ones possess proteinaceous, hair-like appendages called fimbriae or pili. Fim-briae, which are macromolecular structures express-ed on the surface layer of various pathogenic bacteria, are frequently found to mediate attach-ment of the organism to mucosal epithelial cells of animal hosts, including those of the gastrointesti-nal, respiratory and genitourinary tracts and the oral cavity (41). For example, some strains of Escherichia coli preferentially adhere to epithelial cells of urinary tracts (65), while Bordetella pertus-sis, Haemophilus influenzae and Streptococcus pyogenes attach to the epithelial cells of the upper respiratory tract (5, 7, 36). Thus, this process has been postulated to be essential in the pathogenesis of infectious diseases at various mucosal sites, although it is only one of many processes leading to colonization and disease. In addition, fimbriae of indigenous organisms play an important role in the establishment and maintenance of normal mi-crobial floras. Thus, bacterial fimbriae are recog-nized to possess ubiquitous characteristics for ini-tial cell-to-surface and cell-to-cell adherence and colonization in the host that may eventually lead to microbial invasion into the tissues (6, 21, 57). The oral cavity provides various mucosal and solid surfaces and microniches that become colo-nized by microorganisms. The composition of the flora in the mouth differs from site to site and at different times or ages. The characteristics of sub-gingival flora are different from those flora in other sites of the mouth. Evidence indicates that the number of cultivable bacterial species in subgin-gival flora exceeds 300, among which the predomi-nant types are anaerobic, Gram-negative bacterial species including a wide variety of motile organ-isms, especially when inflammation occurs in gin-gival and periodontal areas (20, 37). Periodontal diseases are infectious in nature and induce an inflammatory response in the gingival and underlying supportive periodontal tissue in response to bacterial accumulation in the subgin-gival crevice. This process is complex both mi-crobiologically and immunologically (10). Current evidence implicates Porphyromonas gingivalis, one of the black-pigmented anaerobic Gram-negative rods, as being most frequently associated with active sites of adult periodontitis (34, 66), while A ctinobacillus actinomycetemcomitans, a microaer-ophilic Gram-negative rod, is mainly associated with juvenile periodontitis (60). In addition, a significant, but limited number of cultivable species, including certain species of Prevotella, Treponema, Fusobacterium, Selenomonas, Bacte-roides, Eikenella, etc. may associate with per-iodontal disease (62). Earlier electron microscopic observations of P. gingivalis and related black-pigmented anaerobic rods revealed that these organisms exhibited fine fibrillar appendages (fimbriae) which were arrang-ed peritrichously, emerging from the cell surface (19, 29, 32, 33). This short review will focus on the