Amino acid changes affecting the activity of pneumolysin alter the behaviour of pneumococci in pneumonia

Pneumolysin is a multi-functional toxin produced by Streptococcus pneumoniae. The toxin has distinct cytotoxic activity and complement-activating activity mediated by different parts of the toxin molecule. Mice challenged intranasally with a type 2 pneumococcal strain contract bronchopneumonia and bacteremia [1]. Mice were infected intranasally with isogenic mutants of this strain in which the chromosomal pneumolysin gene carried point mutations affecting either or both properties of pneumolysin. Reduction in either cytotoxic activity or complement activation by pneumolysin decreased the virulence of the mutant pneumococci. However, it was the ability to activate complement that most affected the behaviour of pneumococci in the lungs and associated bacteremia in the first 24 h following infection.