Serotypes
S.pneumoniae normally possesses a capsular polysaccharide that surrounds the cell and shields the bacterium from the host immune system. These polysaccharides are differentiated as ‘serotypes’ and 100 different pneumococcal serotypes have been identified to date.
Research efforts between 1915 to 1945 led to many new discoveries about pneumococci, including the identification of around 80 serogroups in the 1940s. The identification of new capsules is important in terms of understanding pneumococcal biology, and it is directly relevant to vaccine development since current vaccines only include a small number of all possible serotypes. Correct identification of pneumococcal serotypes is therefore fundamental.
The geographic distribution of pneumococcal serotypes is highly variable between and within continents and countries. In Africa, serotypes 14, 6A and 6B account for more than 50% of cases of invasive pneumococcal disease. The current 10- and 13-valent conjugate vaccines provide protection against most of the meningitis-causing serotypes.
