Podcast
Questions and Answers
Which characteristic describes Streptococcus pyogenes?
Which characteristic describes Streptococcus pyogenes?
Which virulence factor of Streptococcus pyogenes is responsible for resisting phagocytosis?
Which virulence factor of Streptococcus pyogenes is responsible for resisting phagocytosis?
What is the function of Streptolysins in Streptococcus pyogenes?
What is the function of Streptolysins in Streptococcus pyogenes?
Which factor of Streptococcus pyogenes is responsible for binding to fibronectin?
Which factor of Streptococcus pyogenes is responsible for binding to fibronectin?
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What differentiates the Streptolysins O and S in Streptococcus pyogenes?
What differentiates the Streptolysins O and S in Streptococcus pyogenes?
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What type of strep causes diseases like pharyngitis and scarlet fever?
What type of strep causes diseases like pharyngitis and scarlet fever?
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Which toxin is responsible for scarlet fever?
Which toxin is responsible for scarlet fever?
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What is the characteristic lesion seen in scarlet fever?
What is the characteristic lesion seen in scarlet fever?
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Which antibody response causes inflammation in rheumatic fever?
Which antibody response causes inflammation in rheumatic fever?
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Which diagnostic test is NOT useful for identifying streptococcal infections?
Which diagnostic test is NOT useful for identifying streptococcal infections?
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What type of medium is used for the growth of Corynebacterium diphtheriae?
What type of medium is used for the growth of Corynebacterium diphtheriae?
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What is the main virulence factor of diphtheria?
What is the main virulence factor of diphtheria?
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Which organ does the toxin of diphtheria primarily affect?
Which organ does the toxin of diphtheria primarily affect?
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What clinical manifestation is characteristic of tonsillar diphtheria?
What clinical manifestation is characteristic of tonsillar diphtheria?
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How is a diagnosis of diphtheria usually confirmed in a clinical setting?
How is a diagnosis of diphtheria usually confirmed in a clinical setting?
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What type of media are cultures made on for the laboratory diagnosis of diphtheria?
What type of media are cultures made on for the laboratory diagnosis of diphtheria?
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Study Notes
Streptococcus Pyogenes (Group A, Beta-Haemolytic Streptococci)
- Gram-positive cocci, some of which are capsulated, facultative anaerobes
- Grow on blood agar, producing complete (Beta) hemolysis
- Catalase negative, Bacitracin sensitive
Virulence Factors
- Adherence factors:
- Fibronectin-binding protein (protein F)
- Lipoteichoic acid (LTA)
- M protein (projections on cell wall)
- Anti-phagocytic factors:
- M protein (resists phagocytosis)
- Hyaluronic acid capsule (immunological mask)
- C5a peptidase
- Spreading factors:
- Streptokinase (Fibrinolysin)
- Streptodornase (Deoxynuclease/DNase)
- Hyaluronidase
- Toxins:
- Streptolysins (Hemolysins, pore-forming cytotoxin)
- Pyrogenic exotoxins (A, B, and C)
- SPE A (erythrogenic toxin, causes rash in scarlet fever)
Diseases Caused by Streptococcus Pyogenes
- Pyogenic (suppurative) diseases:
- Pharyngitis
- Toxigenic diseases:
- Scarlet fever
- Immunologic diseases:
- Rheumatic fever
- Acute glomerulonephritis
Streptococcal Pharyngitis (Strep Throat)
- Characteristics:
- Swollen tonsils
- Purulent exudate
Scarlet Fever
- Characteristics:
- Scarlet, erythematous rash
- "Strawberry" tongue is a characteristic lesion
Post-Streptococcal Diseases
- Rheumatic fever: occurs weeks after local infection
- Acute glomerulonephritis: occurs weeks after skin infections
Diagnostic Tests
- Specimen: throat swab
- Antigen detection tests: ELISA or agglutination tests (rapid)
- Serology (ASO test): for post-streptococcal diseases
Treatment
- All beta-haemolytic group A streptococci are sensitive to penicillin G
- Treatment of scarlet fever: penicillin + antitoxin serum
Corynebacterium Diphtheriae
- Gram-positive rods, non-spore-forming, non-motile
- Club-shaped, giving V, Y, or Chinese-letter appearance
- Have inclusion granules (metachromatic or volutin) seen by methylene blue or Neisser or Albert's stain
- Aerobes, growing on enriched media:
- On Loffler's serum (grayish-white colonies)
- On blood tellurite agar (selective medium, giving black colonies)
Virulence Factors
- Diphtheria toxin: the main virulence factor, produced only by strains infected by bacteriophage (lysogenic)
- Consists of 2 fragments (A, B)
- A is for inhibition of protein synthesis (inactivates elongation factor 2)
Pathogenesis and Clinical Picture
- Tonsillar diphtheria: most common, transmitted by droplets
- Organism does not invade, multiply locally, causing local necrosis with fibrinous exudate, resulting in grayish-white pseudomembrane
- Exotoxin released diffuses to the bloodstream, causing toxaemia, affecting other organs
- Other forms of diphtheria: nasal infection, conjunctival or skin diphtheria (rare, by contact)
Laboratory Diagnosis
- A. Direct smears: stained with Gram, methylene blue, or Neisser stains (negative result cannot exclude diphtheria)
- B. Cultures: made on Loeffler's serum and blood tellurite media
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Description
This quiz summarizes the general characteristics and virulence factors of Beta-haemolytic streptococci, specifically focusing on Streptococcus pyogenes. Learn about their Gram-positive nature, growth conditions, and key virulence factors such as adherence and anti-phagocytic factors.
