Strepto Pyogenes Flashcards Preview

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Flashcards in Strepto Pyogenes Deck (14)
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1
Q

Describe the microbiology of the Streptococci (gram,…)

A

Cocci, string

Gram positive

2
Q

What are the 3 main types of classification of streptococci ?

A
  • By Haemolysis type

- Lancefield classification : by reaction to antibodies due to antigen on cell wall

3
Q

What is the classification of Streptococcus pyogenes ?

A
  • Lancefield group A

- Beta haemolytic

4
Q

What are the 3 types of Haemolysis ? What do they do and look like ?

A

Alpha : partial breakdown of RBC, Viridans (green)

Beta : complete RBC breakdown , Pyogenes (white,pus)

Gamma : non-haemolytic

5
Q

Why does Strepto pneumoniae has a wet and green appearance ?

A
  • Green due to alpha Haemolysis : it’s s Viridans streptococcus
  • Wet :carbohydrate coat ,capsule protecting the bacteria (more virulent)
6
Q

Why is Strepto agalactiae responsible for neonat sepsis and meningitis ?

A

Normal flora of vagina so exposed during birth

7
Q

What are the virulence factor of Strepto pyogenes ?

A
  • Hyaluronic acid capsule
  • Mprotein
  • Adhesins
  • Streptolysins O and S
  • Dnases
  • Hyaluronidase
  • Streptokinase
  • Streptococcal pyrogenic exotoxins
8
Q

What is the role of the Hyaluronic acid capsule of the Strepto pyogenes ?

A
  • Inhibits phagocytosis by neutrophils and macrophages

- Because similar to human Hyaluronate in CT

9
Q

What is M protein and what is its role ?

A
  • long chain of peptides sticking out of bacteria

- resistance to phagocytosis by inhibiting activation of complement pathway on bacteria surface

10
Q

What are the actions of Streptolysins ?

A

-Lysis of RBC, neutrophils and platelets (Haemolysis and decrease immune response )

11
Q

What is the role of streptokinase ?

A

Convert plasminogen in plasmin to dissolve clots

12
Q

What do Streptococcal pyrogenic exotoxins do ? SPE

A
  • cleaves IgG bound to group A strep

- Activate T cell response : SUPERATIGENIC :inflammation

13
Q

What are the criteria of Streptococcal toxic shock syndrome ?

A
  • Deep tissue infection by strep pyogenes
  • Bacteremia
  • Vascular collapse
  • Organ failure
14
Q

What causes Strepto toxic shock ? (Steps)

A
  • Entry of group A in bloodstream
  • SPE stimulate T cells by binding to MHC II APCs and T cell receptors
  • Induction of Cytokines and Lymphokines release : vascular collapse
  • M protein fibrinogen complex formation : Ischaemia and organ failure