Medicine & USMLE

Strep pneumoniae: Overview

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Bacteria - Gram Positive
  1. Staph aureus: Overview
  2. Staph aureus: Presentation
  3. Methicillin-Resistant Staph aureus (MRSA)
  4. Staph saprophyticus
  5. Strep pneumoniae: Overview
  6. Strep pneumoniae: Presentation
  7. Strep viridans
  8. Strep pyogenes: Overview
  9. Strep pyogenes: Presentation
  10. Strep agalactiae
  11. Strep bovis
  12. Enterococcus
  13. Bacillus anthracis
  14. Bacillus cereus
  15. Clostridium tetani
  16. Clostridium perfringens
  17. Clostridium botulinum
  18. Clostridium difficile
  19. Corynebacterium diphtheriae
  20. Listeria monocytogenes
  21. Nocardia
  22. Actinomyces

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