Putative virulence genes in clinical strains of Porphyromonas gingivalis

Objectives: Porphyromonas gingivalis (Pg) is a heterogenous species with subpopulations of various levels of virulence. Previous in vitro studies indicated that virulent and avirulent laboratory Pg strains may be distinguished by specific genes. The purpose of this study was to determine the prevalence of virulence genes in clinical strains of Pg.

Methods: Ninety-seven clinical Pg isolates from patients with periodontitis and 3 laboratory (MCCM00583, MCCM00599, and ATCC55397) Pg strains have been analyzed by PCR for the presence of the following virulence genes: ORF Pg0110 (Glycosyl transferase), Pg0111 (Capsular polysaccaride biosynthesis gene), Pg0117 (Polysaccaride transport protein), Pg0683 (ABC transporter), Pg0742 (Antigen PgaA), Pg0826 and Pg1447 (Transcriptional regulator), Pg0827 and Pg1446 (MATE efflux family protein), Pg0828 and Pg1445 (Truncated RteC protein), Pg1454 (Integrase), Pg1644 and Pg1645 (ISPg5 Transposase), Pg2100 (Immunoreactive 63-kD antigen Pg 102).

Results: In the clinical Pg strains the following prevalence of the analyzed genes was found: Pg0110 (25.8%), Pg0111 (7.2%), Pg0117 (7.2%), Pg0683 (51.5%), Pg0742 (13.4%), Pg0826 (8.2%), Pg0827 (18.6%), Pg0828 (19.6,%) Pg1445 (13.4%), Pg1446 (12.4%), Pg1447 (12.4%), Pg1454 (19.6,%), Pg1644 (82.5%), Pg1645 (95.9%), Pg2100 (41.2%). In the analyzed laboratory strains, only Pg1645 (100%) and Pg0683 (75%) were detected. Based on the frequency of virulence genes, there was no predominant Pg strain in patients with periodontitis.

Conclusions: Clinical Pg strains from patients with periodontitis exhibit a great diversity with regard to the genes analyzed. The genomic plasticity may be promoted by insertion sequence elements like the ISPg5 transposase that has been identified in the vast majority of the strains analyzed.