Fig. 10. Comparison of pneumococcal pneumonia in serotype 1 compared to serotype 2 infection.

In a serotype 1 (ST217/ST3081) infected lung, levels of bacterial lysis are high, resulting in release of high concentrations of the toxin pneumolysin. These high levels of pneumolysin cause damage to tight junctions between epithelial cells and levels of cell cytotoxicity are high. Subsequent damage to lung epithelial cell barriers allows for serotype 1 pneumococci to disseminate from the lungs into the bloodstream and cause bacteraemia. In pneumonia caused by other S. pneumoniae serotypes such as 2 (D39), rates of bacterial lysis are lower and therefore lower concentrations of pneumolysin are released into the lung. This results in lower cell cytotoxicity and reduced damage to cell barriers between lungs and blood, allowing for containment of bacteria within the lungs and therefore no development of bacteraemia.