16 Questions
Which characteristic describes Streptococcus pyogenes?
Facultative anaerobes
Which virulence factor of Streptococcus pyogenes is responsible for resisting phagocytosis?
Hyaluronic acid capsule
What is the function of Streptolysins in Streptococcus pyogenes?
Inducing fever
Which factor of Streptococcus pyogenes is responsible for binding to fibronectin?
M protein
What differentiates the Streptolysins O and S in Streptococcus pyogenes?
O is antigenic, while S is not antigenic
What type of strep causes diseases like pharyngitis and scarlet fever?
Pyogenic
Which toxin is responsible for scarlet fever?
Erythrogenic toxin
What is the characteristic lesion seen in scarlet fever?
Strawberry tongue
Which antibody response causes inflammation in rheumatic fever?
Autoantibody response to M proteins
Which diagnostic test is NOT useful for identifying streptococcal infections?
Gram stain
What type of medium is used for the growth of Corynebacterium diphtheriae?
Loffler’s serum
What is the main virulence factor of diphtheria?
Diphtheria toxin
Which organ does the toxin of diphtheria primarily affect?
Heart
What clinical manifestation is characteristic of tonsillar diphtheria?
Grayish white pseudomembrane in the throat
How is a diagnosis of diphtheria usually confirmed in a clinical setting?
Direct smears stained with Gram or methylene blue
What type of media are cultures made on for the laboratory diagnosis of diphtheria?
Loefflers serum and blood tellurite media
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
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.
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