Streptococcus Pyogenes

Streptococcus Pyogenes

 

Morphology

  • Group A streptococci
  • Gram-positive cocci
  • Arranged in chains.

Biochemical Characterstics

  • Senstivity to bacitracin. (Maxted’s observation).
  • Catalase negative (S aureus is Catalase Positive)
  • CAMP Negative (Group B Streptococci are CAMP Positive)
  • Not soluble in 10% bile.
  • Hydrolyse PYR (Used for Presumptive Diagnosis of S pyogenes)
  • Ferment trehalose but not ribose.

Cultural Characteristics

  • Virulent strains produce ‘matt’ (finely granular) colony
  • Avirulent strains produce ‘glossy’ colonies.
  • Capsulated strains produce mucoid colonies, corresponding in virulence to the matt type.

METHOD OF TRANSMISSION:

  • Respiratory droplets
  • Hand contact with nasal discharge and skin contact with impetigo lesions
  • Pathogen can also be found in its carrier state (anus, vagina, skin, pharynx)
  • Can spread from cattle to humans through raw milk and contaminated foods (salads, milk, eggs)

Antigenic Structure

  1. Polysacchaide capsule:
    1. Composed of hyaluronic acid.
    2. Protect from ingestion and killing by phagocytosis.
    3. Also helps in colonization in the pharynx by binding to CD44
  2. CellWall:
    1. Inner layer made of peptidoglycan.
    2. Middle layer made of carbohydrate (basis of Lancefielil classification).
    3. Outer layer made of protein and lipoteochoic acid. e.g. M Protein T, R.
    4. M protein is basis of Griffith Typing. Inhibit phagocytosis.
    5. Antibody to M is protective.
  3.  Hair-like pilli (fimbria): Important for attachment to epithelial cells.

Antigenic Similarity

  • Antigen of streptococci are similar to normal human cells
  • Streptococcal infection is associated with autoimmune disease like rheumatic fever.
    • Capsular hyaluronic acid —>Synovial fluid
    • Cell wall protein —>Myocardium
    • Group A carbohydrates —> Cardiac valves
    • Cytoplasmic membrane —>Vascular intima
    • Peptidoglycan (mucoprotein) —->Skin antigen

Toxins and Virulence Factors

  •  Hemolysin
    • Oxygen labile
    • Activity only on pour plate
    • Antigenic specific.
    • Cardiotoxic
  • Streptolysin
    • Oxygen stable and serum soluble]
    • Non antigenic
    • Hemolysis on surface
  • Pyrogenic Exotoxin = Erythrogenic = Dick = Scadatinal Toxin:
    • This is superantigen causing TSS.
    • Identify children susceptible to scarlet fever by intradermal injection (Dicktest) and Schultz Charlton Reaction.
    • .Three types : Types A (MC) and Type C are coded by bacteriophage while type B is chromosomal.
  • Streptokinase (Fibrinolysin): Facilitates spread of infection.
  • Spy Lep: A serine protease that cleaves and inactivate IL-8, thereby inhibiting neutrophil recruitment to the site of infections.
  • Deoxyribo nuclease (Streptodornase): Responsible for thin serous character of strep Exudates. Also called as DNAase.
  • Nicotinamide Adenine Dinucleotidase (NAD-ase).
  • Hyaluronidase: Favor spread of infection.
  • Serum opacity factor: Lipoproteinase.
  • Anti Streptolysin O titre used in retrospective diagnosis; > 200 units is significant .

 

Clinical Manifestations of Streptococcus pyogenes

Infections typically begin in the throat or skin. The most striking sign is a strawberry-like rash

  1. Pharyngitis (strep throat):
    1. Sore Throat is the M/C Streptococcal Infection
  2. Localized skin infection (impetigo)
  3. Erysipelas(Superficial + S/C Tissue) and cellulitis (superficial form of cellulitis)
  4. Necrotizing fasciitis
  5. Scarlet fever:Streptococcal Pharyngitis + Rash with Minute Papules (Sand Paper Skin),
    1.  Associated with Circumoral palor + Strawberry Tounge
  6. Streptococcal toxic shock syndrome
  7. Autoimmune-mediated complications(  rheumatic fever and acute postinfectious glomerulonephritis
  8. Genital Infections
    1. Anaerobic Streptococci are most important cause of puerperal sepsis
  9. Bacteremia
    1. Bacteremia , Pneumonia and Toxic Shock Syndrome
  10. Non Suppurative  Complications

 

Acute Rheumatic Fever Acute Glomerulonephritis
Post Throat Infection (Any Serotype) Skin / Throat Serotypes 49, 53-55, 59-64, 1 & 12
Repeated Attacks Common Not seen
Penicillin Prophylaxis Indicated Not indicated
Course – Progressive / Static Self limiting
ASO Titre Raised May or May not (Skin Infection) Raised
Marked Immune Response No Change in Complement Moderate Immune Response with ↓ Complement Level

Lab Diagnosis of Streptococcus pyogenes

  • Acute Pharyngitis – Swab Culture (Gold Standard)
  • Transport Media – Pike’s Media
  • Sheep Blood Agar recommended (As it is inhibitory to H. hemolyticus)
  • ARF and Ac GN retroscpective with ↑ ASO Titres ( ASO > 200)
  • In Ac GN & Pyoderma Anti DNAse and Antihyaluronidase  used for retrospective diagnosis
  • Streptozyme Test :- Passive Haemagglutination Test (Specific and Sensitive for all Streptococcal Infections)

Management of Streptococcus pyogenes

  • Penicillin :- Pharyngitis / Impetigo / Erypsipelas / Cellulitis
  • Penicillin + Empyema Drainage:-Empyema or Pnemonia
  • Penicillin + Clindamycin + Surgical Debridement :-Necrotizing Fascitis / Myositis
  • Penicillin + Clindamycin + i/v Ig :- Streptococcal TSS

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Streptococcus pyogenes  Click Below to Download

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Staphylococcus aureus and Streptococcus pyogenes are SIMILAR in all of the following features EXCEPT one. Pick the INCORRECT statement:
Both produce numerous exotoxins and exoenzymes
Both are Gram-positive cocci
Both cause skin, tissue, and systemic infections
Both are catalase positive

Correct!

Wrong!

Streptococcus pyogenes is -
Gram positive cocci
Gram negative cocci
Gram positive bacilli
Gram negative bacilli

Correct!

Wrong!

False regarding streptococcus pyogenes
Causes necrotizing fascitis
Beta hemolytic
M. protein is virulece factor
Resistant to bacitracin

Correct!

Wrong!

Streptococcus causing rheumatic heart disease is
Streptococcus milleri
Streptococcus mutans
Streptococcus pyogenes
All of the Above

Correct!

Wrong!

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Streptococcus Pyogenes

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Streptococcus pyogenes

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