The pathogenesis of
bacterial infection involves a series of interactions between the virulence determinants of the microorganisms and the immunity of the host. Studies on the molecular structure and immunological properties of pneumococcal
virulence factors have provided general knowledge for the chemical basis of immunogenicity and prevention of
bacterial infection. Antibody responses to PS and
protein antigens can be greatly affected by their physicochemical properties, e.g., molecular size, specific determinants, conformation, etc. Characterization of group 19 pneumolysins and cloning of their ply genes were studied to examine the relationship of ply to virulence. Group 19 pneumococci all contained ply; the disease-isolated types of 19F and 19A appeared to show a higher specific hemolytic activity and yield than the nonpathogenic types, 19B and 19C. Genomic
DNA that contained the ply gene from group 19 strains were analyzed by the polymerase chain reaction (PCR). Type 2
oligonucleotide primers recognized and initiated synthesis of an identical 1.5 kb
DNA fragment in types 2, 19F, 19A, 19B, and 19C. Their sizes of restriction
DNA fragments were also found to be homologous. Thus, group 19 ply genes showed remarkably similar characteristics. A difficult problem in the development of
vaccines against
bacterial diseases is the poor immune response of young children to purified PSs. The efficacy of
pneumococcal vaccine might be improved by supplementation with inactivated
pneumolysin in the form of a PS-
protein conjugate.