Prevalence and distribution of six capsular serotypes of Porphyromonas gingivalis in periodontitis patients

Previous reports have described six serotypes based on K antigens in Porphyromonas gingivalis strains. The purpose of the present study was to investigate the prevalence and distribution of these serotypes in 185 patients with P. gingivalis-associated periodontitis. Polyclonal rabbit antisera, raised against each of the different type strains, were used in double-immunodiffusion and immunoelectrophoresis assays. In addition, a subset of 76 strains was investigated for the presence of capsular structures by means of the India ink and Bruce White staining techniques. These strains were also tested for auto-aggregation in phosphate-buffered saline (PBS). All six K serotypes were present in the study sample. In total, 84 (45.4%) patients were colonized with a K-typeable P. gingivalis strain with a predominance of types K5 (12%) and K6 (23.2%). A correlation was found between arbitrary age categories and the prevalence of currently known K serotypes, which were found in 60% of patients aged 12 to 30 years, in 49% of patients aged 31 to 50, and in 25% of patients aged 51 to 70 years. In the subset of 76 P. gingivalis strains, 32 (42.1%) were K-typeable. Fifty-three strains (69.7%) showed microscopic evidence of encapsulation, suggesting the existence of K serotypes other than K1 to K6. Twenty-one strains (27.6%) auto-aggregated in PBS and were not K-typeable, nor did they show any evidence of encapsulation. It was concluded that the majority of clinical P. gingivalis isolates is encapsulated and that encapsulation is associated with the presence of a K antigen. Auto-aggregation seems to be associated with the absence of a capsular structure and, consequently, the absence of a K antigen.