Evasion Of Host Defences By Pathogen Flashcards
What is the classic infection caused by S. pyogenes?
Impetigo, pharyngitis, tonsillitis, peritonsillar abscess, pneumonia, meningitis, necrotising fasciitis
What toxin-related disease is caused by S. pyogenes?
Scarlet fever
What are the immune-mediated diseases associated with S. pyogenes?
Rheumatic fever, acute glomerulonephritis
What is a characteristic symptom of scarlet fever?
Red strawberry tongue
What are some mechanisms pathogens use to evade the host response?
- Resistance to phagocytosis
- Evasion of complement
- Iron scavenging
- Concealment/variation of antigen
- Modulation/suppression of the immune system
What type of organism is Streptococcus pyogenes?
Non-motile Gram-positive cocci, arranged in chains
What is the carriage rate of S. pyogenes?
15-20%
What is the significance of iron-binding molecules for pathogens?
They allow pathogens to acquire iron, which is essential for growth
What is the role of superantigens in S. pyogenes?
Polyclonal activation of T-cells leading to a massive inflammatory response
What is antigenic variation?
The alteration of surface proteins of a pathogen to avoid recognition by the immune system
What are some virulence factors of Streptococcus pyogenes?
- Pili
- M protein
- SpyCEP
- C5a peptidase
- Hyaluronic acid capsule
- Superantigens
- SpeA
- DNases
- Leukotoxins
- Proteases
- Fibronectin binding protein
- SIC
- LTA
Fill in the blank: Streptococcus pyogenes is also known as _______.
[β-haemolytic, Lancefield group A]
True or False: S. pyogenes is resistant to most antibiotics.
False
What is the function of siderophores in bacteria?
To bind iron from the host to overcome iron starvation
How can organisms evade phagocytosis?
- Destroy chemoattractants
- Destroy opsonising antibodies
- Prevent opsonisation
What is the role of capsules in evading the complement system?
Capsules prevent complement activation
What is a method of antigen concealment used by pathogens?
Intracellular existence, preventing antigen display on the cell surface
What can cause an immune response to fail in the context of S. pyogenes?
Poor fitting antigen leading to no T-cell activation
What is gene switching in the context of antigenic variation?
Switching from expression of one gene to another
What is the main feature of the immune evasion strategy known as camouflage?
Absorbing and coating with host blood glycolipids and proteins
