Staphylococcus aureus

Question 1

Pathogenesis of Staphylococcus aureus?

Answer 1

• adherence via teichoic acid
• uses enzymes like hyaluronidase and staphylokinase (lyses fibrin clots) to tunnel through tissue

Question 2

Virulence factors of Staphylococcus aureus?

Answer 2

• Protein A: binds to portions of IgG & helps protect against opsonization (tagging for elimination) and phagocytosis
• Hemolysins alpha, beta, delta, gamma / leukocidins: destroy cells (RBCs, neutrophils, macrophages, platelets)
• Capsule & Slime layer: hinders phagocytosis by polymorphonuclear leukocytes & aids in adhesion
• Toxins: can be associated more commonly with specific diseases (i.e. TSST-1: Toxic Shock Syndrome toxin-1, enterotoxins, exfoliative toxins)
• Beta-lactamases enzymes: degrade antibiotics

Question 3

What results in clinical manifestations of S. aureus?

Answer 3

organsim proliferation

• abcess formation & tissue destruction
• cutaneous infections, endocarditis, pneumonia, empyema (pus in pleural cavity), osteomyelitis (infection of the bone)\, septic arthiritis

toxin activity

• staphylococcal scalded skin syndrome
• staphylococcal food poisoning
• toxic shock syndrome (i.e. Menstrual Toxic Shock Syndrome)

Question 4

Lab diagnosis of S. aureus?

Answer 4

Gram-stain

• gram-positive cocci in clusters

Culture

1) Blood Agar
- S. aureus: beta-hemolytic
- other Staphyloccus sp: non-hemolytic
2) Mannitol-salt Agar (contains 7.5% NaCl)
- a selective media
- most other commensal skin bacteria are inhibited by high salt
- phenol red in agar turns yellow (Mannitol-fermenting)