Pathogenicity and Immunochemical Properties of a Serotype Specific Antigen Defective Mutant of Actinobacillus actinomycetemcomitans

Abstract

A spontaneous cupsular-like serotype-specific antigen defective mutant of Actinobacillus actinomycetemcomitans strain Y 4 (serotype b) was isolated. Immunodiffusion test showed that the autoclaved extract from A. actinomycetemcomitans Y 4 Cap⁺ formed a single preciptin band with anti-Y 4 Cap⁺ serum and a monoclonal antibody to serotype b-specific antigen (MAb S 5). The autoclaved extract from uncapsulated mutant Y 4 Cap^- did not form any preciptin band with anti-Y 4 Cap⁺ serum and MAb S 5. Western blott analysis showed that MAb S 5 reacted with diffuse high-molecular -weight bands in the whole cells from Y 4 Cap⁺, but did not in the whole cells from Y 4 Cap^-. To determine the virulence of Y 4 Cap⁺ and Y 4 Cap^-, C 3 H/HeJ mice were intraperitoneally infected with whole cells of both strains. Among 15 mice infected with 7.5 x 10¹⁰ CFU of Y 4 Cap⁺, 1.1 mice died within 24 hours, but the mice infected with the same dose of Y 4 Cap^- did not die. MAb S 5 inhibited the lethality of Y 4 Cap⁺ in mice. These results suggest that serotype-specific antigen of A. actinomycetemcomitans may play a critical role in the pathogenesis of the organism.