Analysis of the capsular polysaccharide biosynthesis locus of Porphyromonas gingivalis and development of a K1-specific polymerase chain reaction-based serotyping assay

Background and Objective: Porphyromonas gingivalis is a gram-negative obligate anaerobe that is strongly associated with severe periodontitis. Previous reports showed an association of P. gingivalis capsular polysaccharide with virulence. The K1 capsular polysaccharide was found to be more immunostimulatory than the other serotypes. Our objective was to explore the genetic background of the capsule biosynthesis (K-antigen) locus in a representative group of K1 serotype strains.
Material and Methods: We used restriction fragment length polymorphism, polymerase chain reaction (PCR) and DNA sequencing to study the capsular polysaccharide locus in P. gingivalis K1 strains. For serotyping by double immunodiffusion and PCR we used 32 strains of P. gingivalis, including strains of all six known K serotypes.
Results: All tested K1 strains showed high conservation of the capsular polysaccharide locus, although a DNA re-arrangement was found in two strains. Based on this information a K1-specific PCR-based serotyping assay was designed. The specificity and sensitivity of this test were confirmed using non-K1 P. gingivalis serotypes.
Conclusion: The capsular polysaccharide locus of P. gingivalis is conserved but may vary slightly among K1 strains. The new K1 serotyping assay presented here is much faster than double immunodiffusion and can detect K1 strains in a very selective and sensitive way. This method may therefore be clinically relevant in the detection of the virulent P. gingivalis K1 serotype.