Strep pneumoniae: Overview


Streptococcus pneumoniae Overview

  • Gram + cocci in pairs (diplococci)
  • Lancet-shaped
  • Alpha-hemolytic
    • partial or “green” hemolysis on blood agar
  • Encapsulated
    • Causes bacteremia/sepsis in patients with sickle cell disease (functional asplenia) vs. asplenic patients
    • Main virulence factor; not pathogenic without capsule
  • IgA protease
    • cleaves lgA at its hinge region (yielding Fab and compromised Fc fragments)
    • Reduced functional IgA increases bacterial adherence to mucosal membranes
  • Bile-soluble
    • Exhibits cell lysis in the presence of bile
    • In contrast vs. strep viridans, which is bile-resistant
  • Optochin sensitive
    • In contrast vs. strep viridans, which is optochin-resistant