Group A Strep

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  1. Group Character
    • Gram positive cocci that grow in chains
    • No catalase
    • Blood agar
    • Beta hemolysis - clear zones around colonies in blood agar; classified by carbohydrate Ag (lancefield groups)
  2. Structure
    • Cell wall built upon peptidoglycan matrix
    • M protein: fibrillar coiled-coil molecule like myosin; extremely diverse in distal ends, conserved in middle portions; Ag receptor, binds fibrinogen, factor H, and others, and provides scaffold for LTA in pathogenesis
    • LTA: binds to cell receptors
  3. Exotoxins
    • Streptolysin O: pore-forming, antigenic which is basis of ASO test
    • SuperAg toxings: 10% of GAS produce these; similar to Staph SuperAg
  4. Epidemiology
    • Phygnitis: Most common cause in school age kids; person to person transmission via coughing, sneezing, etc...; 1-4 week duration
    • Impetigo: Minor skin truame with GAS colonization
    • Wound infections: iatrogenic
    • STTS: Severe soft tissue invasion; rapid progression to death
  5. Pathogenesis
    • Nasopharynx invasion
    • M protein provides scaffold for LTA to reach binding site (in skin, M binds directly)
    • Protein F - adherence to langerhans cells
    • M protein prevents phagocytosis via binding factor H
    • STSS: massive cytokine release
    • ARF: Type II hypersensitivity; Ab to M protein
    • Acute glomerula nephritis: Type III hypersensitivity
    • Type specific immunity; type specific IgG activate complement via classical pathway
  6. Clinical Manifestations: Acute infection
    • Pharyngitis: between 5-15 yo; acute sore throat, malaise, fever, headache; tonsillar pillars, uvula, soft palate; erythema, pus; cervival adenopathy; Self-limiting; can spread to form abcesses
    • Impetigo: small vesicle w/ erythema; enlarges, yellow crust; 2-5 yo kids
    • Erysipelas: Spreading erythema w/edema and fever
  7. Clinical Manifestations: StrepSAgs
    • Scarlet Fever: buccal mucosa, temples, cheeks are deep red with circumural rash; strawberry tongue; sandpaper rash on second day of illness
    • STSS: Begin at any site of infection; vague myalgia, chills, severe pain at site of infection; necrotizing fasciitis and myonecrosis; Continues with nausea, vomiting, hypotension, shock and organ failure
  8. Post Strep Sequelae
    • ARF: Fever, carditis, subcutaneous nodules, chorea, and polyarthritis; murmurs, enlargement; 3 weeks post strep pharyngitis; last 2 weeks to 3 months; repeat attacks cause progressive heart damage
    • Acute GN: Disease of childhood; begings 1-4 weeks after pharyngitis and 3-6 weeks post skin infection
  9. Diagnosis
    • Clinical
    • Blood agar with Beta hemolysis
    • Serologix groupig
    • Rapid strep test: group A Ag on throat swab
    • ASO titers in ARF
  10. Treatment
    • Pencillin G
    • Treat within 10 days to prevent ARF
    • Prophylaxis for recurrent ARF during ages 5-15 and during certain procedures
Card Set
Group A Strep
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