Staphylococcus aureus

From IDWiki
Staphylococcus aureus



  • Facultative anaerobic, Gram-positive coccus
  • Catalase-positive and coagulase-positive
  • Microscopy: groups or clusters ("cluster of grapes")
  • Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar


Virulence Factors

  • Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells)
  • Membrane-damaging toxins (hemolysins), including Panton-Valentine leukocidin (PVL)
  • Exfoliative toxins (A and B) which disrupt the junction between epidermal cells, causing scalded skin syndrome
  • Superantigens that bind to MHC molecules and T-cell receptors, leading to release of huge amounts of cytokines

Antibiotic Resistance

  • Mechanisms of resistance are myriad
  • Common ones:
    • bla gene encodes penicillinase, conferring resistance to penicillin
    • mecA encodes PBP2a, conferring broad β-lactam resistance (MRSA)
    • vanA on a plasmid confers vancomycin resistance (VRSA)

Clinical Manifestations


Skin and Soft Tissue Infections

  • Boils and carbuncles
  • Cellulitis, usually purulent

Scalded-Skin Syndrome

  • Aka Ritter disease
  • Caused by exfoliative toxin A or B
  • Essentially bullous impetigo
  • Sunburn-like, bullous rash that can lead to skin loss (most common in kids with Staph infections of the nasopharynx or skin)


Infective Endocarditis

Other Infectious Syndromes

Superantigen-Related Syndromes

Staphylococcus-Associated Glomerulonephritis


  • Duration depends on clinical syndrome

Methicillin-Susceptible Staphylococcus aureus (MSSA)

Methicillin-Resistant Staphylococcus aureus (MRSA)