Genotypic and phenotypic characterization of Porphyromonas gingivalis in relation to virulence

Abstract

The present thesis was designed to increase the knowledge on the role of pathogenic potential of Porphyromonas gingivalis as a putative periodontal pathogen. P. gingivalis was selected to be the model species for periodontal pathogens based on expressing a number of significance virulence factors and on the considerable genetic heterogeneity of this species. The hypothesis of the present studies was that the pathogenic potential of P. gingivalis differs among this species and that certain clonal type of P. gingivalis express more pathogenic capacity than the others. The over all aim of this thesis was to investigate the virulence properties and the pathogenic capacity of species Porphyromonas gingivalis. • Phenotypic heterogeneity of P. gingivalis species was evaluated by colony morphology, biochemical tests, enzymatic profiles, gas-liqid chromatography, antibiotic tests, SDS-PAGE profiling for cell wall protein and serotyping by monoclonal antibodies reactivity (study I). • The diversity of whole chromosomal DNA among P. gingivalis species was evaluated by using amplified fragment length polymorphism (AFLP) and random amplified polymorphic DNA (RAPD) genotyping assays (study II). • The variations of specific virulence biotypes based on fimA, rgpA and kgp genes and capsular K-antigens in P. gingivalis species were evaluated (study III). • The interaction of P. gingivalis species with epithelial and PMN cells was evaluated by KB epithelial cell binding assay (study IV). The present thesis demonstrated that: – P. gingivalis strains showed a strong homogeneity in relation to biochemical tests and antibiotic susceptibility. Furthermore, the majority of P. gingivalis strains displayed monoclonal antibodies (MAbs) serotype A, while serotype B was unusual among P. gingivalis strains (Study I).

– P. gingivalis isolated from Swedish subjects with periodontitis and periodontal abscess exhibited a wide variety of genotypes with weak clustering pattern. No predominant genotype at the whole chromosomal DNA level was present among these P. gingivalis (Study II).

– Chronic periodontitis is not associated with a particularly virulent genotype of P. gingivalis. A highly virulent genotype (e.g. strain W83) of P. gingigvalis can be detected in certain periodontitis subjects (Study III).

– All strains showed binding capacity to host epithelial cells. Encapsulated P. gingivalis compared to non-encapsulated strains displayed a significantly lower binding capacity to host cells. No significant difference in binding and invasion was found between specific virulent genotypes. Thus, the two major virulence groups within P. gingivalis were mainly related to the presence/absence of a capsule structure of this organism (Study IV).