USMLE

Staph aureus: Presentation

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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

Staph Aureus Presentation

  • Commonly colonizes the nares, ears, axilla, and groin 
  • Note: Staphylococcus aureus is a constituent of the normal skin flora
    • Most common cause of nosocomial (hospital-related) infections, especially with intravascular devices or IV drug use (access via skin)
  • Inflammatory disease
    • Skin infections
      • E.g. impetigo, cellulitis, skin abscesses
    • Pneumonia
      • causes superimposed bacterial pneumonia on viral infections 
    • Acute endocarditis
      • Common in IV drug users
      • Tricuspid valve is usually affected
      • Patients may develop multiple septic emboli in lungs, which can cause pulmonary infarcts
    • Septic arthritis
      • Most common cause of septic arthritis
      • More common in IV drug users 
    • Osteomyelitis
      • Adhesion to collagen is the main virulence factor of Staphylococcus aureus in osteomyelitis. 
      • Most common cause of osteomyelitis overall
  • Toxin-mediated disease
    • Toxic shock syndrome (TSST-1)
      • TSST-1 is a superantigen that crosslinks MHC II and T-cell receptor, resulting in polyclonal T-cell activation
      • fever, vomiting, rash, desquamation, shock, end-organ failure
        • Toxic shock syndrome (TSS) is caused by Staphylococcus aureus. TSS presents with fever, vomiting desquamation, and hypotension.
      • TSS results in ↑ AST, ↑ ALT, ↑ bilirubin. 
      • Associated with prolonged use of vaginal tampons or nasal packing
      • Compare with Strep pyogenes TSS: toxic shock-like syndrome associated with painful skin infection 
    • Scalded skin syndrome (exfoliative toxin)
      • Exfoliative toxin destroys keratinocyte attachments in the stratum granulosum
      • Typically seen in newborns, children, adults with renal insufficiency 
    • Gastroenteritis/food poisoning (enterotoxin)
      • Preformed enterotoxin
        • Heat stable, not destroyed by cooking
      • Short incubation period (2- 6 hr), followed by vomiting and abdominal cramps (more common) and diarrhea (rare)
      • associated with consumption of certain precooked foods, dairy products, custard, and mayonnaise that sits at room temperature for an extended period of time (e.g. picnic, potluck)