Association of the rgpB gingipain genotype to the major fimbriae (fimA) genotype in clinical isolates of the periodontal pathogen Porphyromonas gingivalis

Abstract

Background: Porphyromonas gingivalis produces outer membrane-attached proteins that include the virulence-associated cysteine proteinases RgpA and RgpB (Arg-gingipains) and Kgp (Lys-gingipain). The gingipains provide P. gingivalis with a general proteolytic tool for degradation of proteinaceous nutrients for growth. They are also essential for the processing and maturation of the major fimbriae (FimA) which are important in facilitating bacterial adhesion to host tissues. FimA has been characterized as an important virulence factor for P. gingivalis, and many studies, both animal experiments and clinical investigations, have characterized fimA genotypes II, Ib, and IV to be associated with disease (periodontitis and cardiovascular disease) while genotypes I, III, and V represent avirulent strains. The relationship between virulence and gene variation of the rgpB gene has not been investigated extensively. However, nucleotide variations of the rgpB gene result in four amino acid substitutions in the catalytic domain identifying five different rgpB genotypes. They are named according to the different amino acid sequences in the primary protein structure of RGPB and named NYPN, NSSN, NSSK, NYPK, and DYPN (Beikler et al. 2005). Aim: The aim of the present study is to elucidate a possible relationship between fimA virulent and avirulent genotypes to the corresponding rgpB genotypes. Methods: The total length of the rgpB (2212 bp) and fimA genes (1140 bp) from 20 clinical isolates was sequenced. Primers for pcr and sequencing of the genes were selected according to earlier investigations. Results: The rgpB genotypes, NSSN and NYPN (n=2 and 6, respectively), were detected in the fimA II genotypes of P. gingivalis, while NSSK was detected in one fimA Ib genotype in the population. For the eight fimA IV genotypes, five NSSK and three NSSN rgpB genotypes were detected. In two fima I genotypes were detected one DYPN and one NYPN of the rgpB variants, while one fimA III genotype was associated with NSSK. Conclusion: The rgpB genotypes NSSN, NYPN, NSSK of P. gingivalis may be associated with the virulent fimA genotypes II, Ib and IV, indicating a possible connection to their virulent properties.