Streptococcus pneumoniae

Abstract

Infections caused by Streptococcus pneumoniae (pneumococcus) are a major cause of mortality throughout the world. This bacteria is a causative agent for community acquired pneumonia, bacteremia, acute otitis media, and meningitis. Its major disease burden is in children, the elderly, and patients with HIV and other immuno-suppressive conditions. The 23-valent capsular polysacchride vaccine is useful in adults but fails to protect those at highest risk of disease at the youngest and oldest ages. Although the current 7-valent conjugate vaccine is effective against invasive diseases caused by the vaccine-type strains, however, S. pneumoniae can be divided into more than 90 serotypes according to the immunochemistry of their capsular polysaccharide, so the vaccine coverage could be limited by invasive nonvaccine-serotypes in vaccinated individuals. Several pneumococcal proteins have been under investigation as potential vaccine candidates including pneumococcal surface protein A (PspA), which is a virulence factor expressed by all clinical S. pneumoniae isolates. This review summarizes some of antigenic determinants that are being studied in the level of experimental models and/or clinical trials for their potential to induce protective immune responses. Some of these markers are located on the bacterial cell surface and anchored to the cell surface structures by well-characterized mechanisms.