Strep pyogenes

Question 1

General

Answer 1

• Colonize Nasopharynx
• Spread by respiratory droplets
• Asymptomatic carriage common in children
• Lancefield Group A (GAS)

Question 2

Morphology

Answer 2

• Gram-Positive
• Cocci
• Long Chains
• Encapsulated (H.A)

Question 3

Cultivation

Answer 3

• B-hemolytic
• White colonies
• 1-2mm pinpoint colonies

Question 4

Non-toxic Virulence Factors

Answer 4

• H.A Capsule, non antigenic
• M-Protein (antigenic mimicry)
• Streptokinase (plasmin act., fibrinolysis)
• DNAse
• Hyaluronidase
• C5a peptidase (prevents opsonization)

Question 5

Toxic Virulence Factors

Answer 5

• Streptolysin-S: heat-labile
• Streptolysin O: B-hemolysis (heat-stable)
• Streptococcal Pyrogenic Exotoxins (SPEs) superantigens

Question 6

Streptococcal Pyrogenic Exotoxins (SPEs)

Answer 6

• SPE-A / C: Scarlet fever, TSST-like
• SPE-B: Necrotizing Fasciitis

Question 7

Invasive pyogenic Diseases

Answer 7

• Pharyngitis/Tonsilitis (strep)
• Sinusitis & Otitis media
• Puerperal fever (postpartum sepsis)
  (- meningitis)

Question 8

Skin & soft tissue Diseases

Answer 8

• Impetigo
• Erysipelas (most common)
• Cellulitis (deeper, ct)
• Pyoderma (round black ulcers)
• Necrotizing Fasciitis

Question 9

Erysipelas

Answer 9

Inflammation of Dermis & large red inflamed area with sharp edge & fever

Question 10

Toxin-mediated Diseases

Answer 10

• Scarlet Fever
• Streptococcal TSS (more lethal than staph aureus)

Question 11

Post-Streptococcal Diseases

Answer 11

1-5 weeks after due to immune resp.
- Acute Rheumatic Fever
- Acute Glomerulonephritis
- Rheumatoid Arthritis

Question 12

Acute Rheumatic Fever

Answer 12

• Molecular mimicry of M-protein
• Similar to Cardiac Myosin
• Endo/Myo/Peri-carditis = Pancarditis
• JONES criteria: Joints, Heart, Nodules, Erythema marginatum, Sydenham/s Chorea (jerking)

Question 13

Acute Glomerulonephritis

Answer 13

• Type II hypersensitivity reaction
• Antigen-Antibody complexes deposit in glomeruli
• Triggered inflammation, destruction
• Edema, Hypertension, Hematuria, Proteinuria

Question 14

Microbiological Diagnosis

Answer 14

• Catalase Negative
• Bacitracin Sensitive
• CAMP Negative
• ASO-titer (anti-streptolysin-O)

Question 15

Treatment

Answer 15

Penicillin!
(Macrolides if allergic - erythromycin)