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.

The class 3 porin proteins of Neisseria meningitidis stimulate bactericidal antibodies and express serotypespecific antigenic epitopes. Sequence analysis of porB genes for the class 3 proteins revealed regions of variability that map to surface-exposed loops. To evaluate the relationship between serotype and variableregion (VR) genotype, sequences from the 11 class 3-expressing serotype strains and 3 additional serotype 4 strains were analyzed by molecular techniques. Multiple-sequence alignment revealed a limited number of unique sequences at each of four VRs (VR1 to VR4), ranging from four unique sequences at VR1 to seven sequence patterns at VR2 and VR4. Serotype-specific VR sequences were found in each of the four VRs, suggesting that each VR has immunologic importance. Five serotypes had at least one VR sequence that was unique. Three serotypes which had sequences in common with other serotypes at each VR were distinguished by examining multiple VRs. Serotype 3 was identical to serotype 19 at each VR, and serotype 8 was identical to serotype 18 at each VR. Serotypes 4 and 21 were identical at VR1 and significantly different at VR3 and VR4. A subpopulation of serotype 4 strains with a unique VR2 sequence was identified. The serotypes which were grouped with closely related or identical sequences at one VR were grouped with different serotypes at other VRs consistent with the pattern of genetic mosaicism described for the porA (class 1 protein) gene. Hybridization assays demonstrated the ability to identify VR genotypes and distinguish serotypes using biotin-labelled oligonucleotide probes. This information may be useful in strain selection for vaccine development, in epidemiologic studies to determine the prevalence of the individual VR genotype (especially among nonserotypeable strains) and, combined with PCR, in the identification of culture-negative suspected meningococcal cases. Neisseria meningitidis causes both endemic and epidemic meningitis and septicemia worldwide. Epidemic group A meningococcal disease occurs at rates of 100 to 500 cases per 100,000 people per year. Rates of endemic disease, primarily caused by groups B and C, range from 1 to 3 cases per 100,000 people and increase to 10 to 50 cases per 100,000 people per year during outbreaks. A serotype 15 group B clone has been responsible for outbreaks in northern Europe, and a serotype 4 clone has been responsible for epidemic group B disease in Brazil and Cuba (18). Currently, capsular polysaccharide vaccines are available only for serogroups A, C, Y, and W-135. The group B capsular polysaccharide is poorly immunogenic and is chemically identical to the carbohydrate moiety of the fetal neural cell adhesion molecule (5), so the feasibility of a group B-specific conjugate vaccine has been questioned (5, 27). Also, the polysaccharide vaccines currently available are not useful in very young children, who constitute the population with the highest attack rates. The meningococcal outer membrane proteins (OMPs) are currently under investigation as a...