Pathogenic Factors of P. gingivalis and the Host Defense Mechanisms

Periodontal diseases are the inflammatory diseases triggered specifically by some selected microorganisms, i.e., periodontopathic bacteria, accumulated in and around the gingival crevice. Among periodontopathic bacteria, Porphyromonas gingivalis, a black-pigmented gram-negative anaerobic rod, has been implicated as a major pathogen of chronic periodontitis (Hamada et al., 1991; Lamont & Jenkinson, 1998). Recent studies using DNADNA hybridization that permits the examination of large numbers of species in large numbers of plaque samples also indicated the increased prevalence of P. gingivalis as well as other ‘red complex species’ (P. gingivalis, Treponema denticola and Tannerella forsythensis) in the subjects with chronic periodontitis (Socransky & Haffajee, 2002). However, it is also evident that the colonization of the putative pathogenic bacteria in subgingival plaque is not sufficient for the initiation/onset of periodontitis, since most periodontopathic bacteria including P. gingivalis may also be present at sound sites (Haffajee et al., 2009). Thus, the onset and progress of chronic periodontitis is based on the balance between the pathogenesis of the periodontopathic microorganisms and the host-defense against them (host-parasite relationship).