Question
Enumerate four infections produced by streptococcus pyogenes and the virulence factors.
Answer
Four infections produced by Streptococcus pyogenes (Group A Streptococcus) and associated virulence factors:
- Pharyngitis (streptococcal sore throat) — mediated by M protein (anti-phagocytic surface protein, mediating adherence and immune evasion) and hyaluronic acid capsule.
- Impetigo/pyoderma — mediated by surface adhesins and streptolysin O/S (haemolysins causing local tissue damage).
- Scarlet fever — mediated by pyrogenic (erythrogenic) exotoxins (superantigens, produced by lysogenized strains, causing the characteristic rash and systemic toxicity).
- Rheumatic fever (a non-suppurative sequela, following pharyngitis) — mediated by M protein, via molecular mimicry between the M protein and cardiac tissue antigens, triggering the autoimmune cross-reactive damage characteristic of this condition.
(Other valid examples: necrotizing fasciitis/toxic shock-like syndrome — mediated by superantigen exotoxins (e.g., SPE-A) causing massive cytokine release; post-streptococcal glomerulonephritis — immune-complex mediated, another non-suppurative sequela.)
Other key virulence factors of S. pyogenes: Streptokinase (fibrinolysin, aiding spread through tissue by dissolving fibrin clots), hyaluronidase (“spreading factor,” breaking down connective tissue hyaluronic acid), DNase (streptodornase), and C5a peptidase (degrades complement-derived C5a, impairing neutrophil chemotaxis).