Streptococcus pneumoniae


  • Streptococcus pneumoniae is a Gram-positive diplococcus with polysaccharide capsule, which is demonstrated by Quellung reaction or capsular swelling when antibodies bind to capsular polysaccharide antigen.
    • Known as the pneumococcus for its role as the most common cause of lobar pneumonia.
    • Historically dubbed ’Captain of the Men of Death’ by Sir William Osler, since he considered the pneumococcus to be the sole cause of pneumonia, and borrowed from John Bunyan’s description of tuberculosis.
  • Ecologic niche is the nasopharynx, the pneumococcus colonizes 5-10% of adults and 20-40% of children.
    • S. pneumoniae is a definite pathogen when isolated from sterile site, e.g,, blood, CSF, pleural or joint fluid.
    • Probable pathogen in respiratory specimens (Gram stain or culture) or postive urine antigen in setting of pneumonia.

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Last updated: October 19, 2022