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Introduction
  • Classification
    • Bacteria
      • Gram-positive cocci
        • Staphylococcus
          • Staphylococcus aureus
  • Pathogenesis
    • transmission
      • hands
      • sneezing
      • surgical wounds
      • contaminated food
        • custards
        • mayonnaise / potato salad
        • canned meats
    • predisposing factors for infection
      • surgical wounds
      • foreign body
        • tampons
        • surgical packing or sutures
      • severe neutropenia
      • IV drug abuse
      • chronic granulomatous disease
      • cystic fibrosis
    • reservoir
      • normal flora of nasal mucosa or skin
      • 25% of population are carriers
    • molecular biology
      • protein A
        • binds Fc component of IgG, forcing variable region to face away from bacterium
          • inhibits phagocytosis
          • inhibits complement fixation
      • enterotoxins
        • fast acting
        • heat stable
      • toxic shock syndrome toxin-1 (TSST-1) superantigen 
        • binds MHC II and T-cell receptor
        • results in polyclonal T-cell activation
      • coagulase
        • converts fibrinogen to fibrin clot
      • exfolatins
        • skin-exfoliating toxins
        • involved in scalded skin syndrome
Diseases
  • Gastroenteritis
    • food poisoning
      • salty foods and custards
    • nausea/vomiting, abdominal pain, diarrhea 2-6 hours after ingesting toxin
    • caused by enterotoxins A-E preformed in food
    • symptoms start and end quickly
  • Infective endocarditis (acute)
    • fever, malaise, leukocytosis, heart murmur
    • due to fibrin-platelet mesh
  • Abscesses and mastitis
    • subcutaneous inflammation
    • due to coagulase
    • liver abscesses via hematogenous spread
  • Toxic shock syndrome
    • desquamating rash
      • especially on palms and soles
    • fever, hypotension
    • multiorgan failure
    • caused by TSST-1
  • Impetigo 
    • erythematous papules to bullae
    • due to coagulase, exfoliatins
  • Scalded skin syndrome
    • infants and children
    • epidermal peeling
    • due to exfoliative toxin
      • epidermolytic toxins A and B against desmoglein 1 in stratum granulosum
  • Pneumonia 
    • typical, acute, productive, rapid onset
    • nosocomial pneumonia
    • due to coagulase, cytolysins
    • can result in empyema
      • pus in the pleural space
  • Surgical infections
  • Osteomyelitis
    • the most common overall cause of osteomyelitis
      • also associated with prostheses, neonates
  • MRSA (methicillin-resistant S. aureus) infection
    • important cause of serious nosocomial and community-acquired infections
    • resistant to β-lactams due to altered penicillin-binding protein
Laboratory
  • Coagulase positive
  • β-hemolytic
  • Small yellow colonies on blood agar
  • Ferments mannitol
Treatment
  • Nafcillin/oxacillin
  • MRSA
    • vancomycin
    • clindamycin
    • TMP-SMX
  • VRSA
    • quinupristin/dalfopristin
  • Gastroenteritis is self-limiting
 

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