Pneumolysin
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Pneumolysin is a virulence factor of the Gram-positive bacteria Streptococcus pneumoniae.[1]

It is a pore-forming toxin of 53 kDa composed of 471 amino acids.[2] It has a range of biological activity, including the ability to lyse[3] and interfere with the function of cells and soluble molecules of the immune system.[4]
Released pneumolysin will aid the bacteria during colonization by facilitating adherence to the host,[5] during invasion by damaging host cells,[6] and during infection by interfering with the host immune response.[7]
The presence of pneumolysin in sputum,[8] urine,[9] CSF[10] and blood[11] can be indicative of an S. pneumoniae infection.