The Common Protein Agglutinogen of Staphylococcus Aureus

A protein agglutinogen common to the internationally recognized serotypes of Staphylococcus aureus is described. Sera of all human subjects studied, healthy or infected, possess a high and fairly uniform level of antibodies against this agglutinogen. The agglutinin is concentrated in commercial human γ-globulin and is deficient in the blood of agammaglobulinemic children. No immunizing agent has been found which will regularly increase agglutination titers in man to a significant degree, although some increase has been induced in rabbits. Serum absorbed with the pure protein agglutinogen shows decreased agglutination titer against all serotypes but is not deprived of its phagocytosis promoting power.

The Common Protein Agglutinogen of Staphylococcus Aureus

Staphylococcal agglutinogen was extracted from undigested cell walls and purified through carboxymethyl (CM)-cellulose column chroma tography and molecular sieving by Sephadex G-75. The sedimentation patterns of ultracentrifugation showed a high degree of homogeneity of the purified agglutinogen. The sedimentation constant is 1.6 S, the diffusion constant is 11.6 × 10-7 cm2/sec, and the molecular weight is 13,200. It showed single line precipitation reactions with human and rabbit antisera in agar gel diffusion and immunoelectrophoresis. From the nitrogen content, ultraviolet absorption, and sensitivity against digestion by proteolytic enzymes, it was shown that the agglutinogen is a protein. Jensen's antigen A contains the agglutinogen.

Some Serological Properties of Staphylococcal Cells and Cell Walls

The present studies indicate that Staphylococcus aureus strain 18Z contains at least seven antigenic components, and the cell walls possess at least two. Among these components, one protein antigen which has positive electric charge at pH 7.4 is mainly contained in the cell walls.

It was also shown that the virulent strain and the avirulent mutant strain contained the same antigenic components. However, the interesting question—whether or not the virulent strain may possess an antigen which is not contained in the avirulent strain— could not be settled. It is of course quite possible that an antigenic component which is responsible for virulence is not extractable by the methods described above.

Dr. Gunnar Haukenes has isolated a carbohydrate from Staphylococcus aureus which he considers to be group-specific and identical with the A carbohydrate of Wieghard and Julianelle (7). Dr. Haukenes has found this carbohydrate in the 18Z parent strain and its several mutants (Personal communication from Dr. Per Oeding).

An arguable hypothesis is that the difference in virulence between 18Z-D and 18Z-A and 18Z-C is dependent upon an extracellular cytopathogenic factor; no evidence for this hypothesis was obtained by Kapral and Li (1). Perhaps a more probable hypothesis is that strain 18Z-D possesses some subtle metabolic defect of unknown nature.