Clonality of Porphyromonas gingivalis, Prevotella intermedia and Prevotella nigrescens isolated from periodontally diseased and healthy sites.

Black-pigmented anaerobes have been implicated as major pathogens in the aetiology of adult periodontitis but these organisms are also found in healthy sites. This study aimed to examine the relationship between genotypes of black-pigmented anaerobes and disease status of periodontal sites using restriction endonuclease analysis (REA) and ribotyping. The main black-pigmented species recovered from sites were Porphyromonas gingivalis, Prevotella intermedia and Prevotella nigrescens. Each of the 58 subjects investigated harboured distinct genotypes of these three species. Most subjects appeared to be colonized by a single genotype of P. gingivalis and Pr. intermedia, whereas multiple types of Pr. nigrescens colonized many individuals. Plasmids were only found in a few Pr. nigrescens strains. No association was found between the disease status of sites and any specific or group of genotypes of either species or presence of a plasmid. Since the same genotypes of P. gingivalis, Pr. intermedia and Pr. nigrescens were found at both diseased and non-diseased sites in a subject, adult periodontitis is not explained by the presence of specially virulent clones of these organisms. Their role in periodontitis, therefore, is likely to be opportunistic.