Molecular basis for virulence in experimental listeriosis : role of cell surface antigens

Abstract

Knowledge concerning the nature of microbial surface components and their role in host-parasite interactions is, in many cases, crucial to an understanding of pathogenicity. While a number of virulence factors, hemolysins and toxins have been reported for the bacterium Listeria monocytogenes none have been able to adequately explain this organisms ability to grow and metabolize in the phagocytic macrophage. Preliminary investigations using various soluble antigens and corresponding antisera have revealed the possibility of a surface protein antigen on L. monocytogenes. Because of the importance of surface antigens in other disease producing organisms and since there is little information on listerial surface components experiments to isolate and study this material were initiated. This study describes the detection, isolation, purification and preliminary biochemical characterization of this surface antigen. The cell surface antigen was obtained from whole cells or cell walls by extraction with 1% Triton X-100 in Phosphate buffer pH 7.4. Partial purification was achieved by chromatography on DEAE-cellulose. The cell wall protein antigen is heat labile, in that it cannot react with specific antibody after being heated above 56°C for 60 minutes. It is trypsin insensitive and pepsin sensitive. The cell wall protein antigen has been extracted from all strains and serotypes examined and there appears to be no correlation with the presence or absence of this antigen with virulence. It was also demonstrated that relative content of this antigen by selected virulent and avirulent strains, as determined by rocket immunoelectrophoresis, gave no indication that this antigen was involved in virulence. Attempts to isolate mutants lacking the surface antigen, as a definitive assessment of its role in virulence were unsuccessful.