Strepto Pyogenes

Question 1

Describe the microbiology of the Streptococci (gram,…)

Answer 1

Cocci, string

Gram positive

Question 2

What are the 3 main types of classification of streptococci ?

Answer 2

• By Haemolysis type

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

Question 3

What is the classification of Streptococcus pyogenes ?

Answer 3

• Lancefield group A

- Beta haemolytic

Question 4

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

Answer 4

Alpha : partial breakdown of RBC, Viridans (green)

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

Gamma : non-haemolytic

Question 5

Why does Strepto pneumoniae has a wet and green appearance ?

Answer 5

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

Question 6

Why is Strepto agalactiae responsible for neonat sepsis and meningitis ?

Answer 6

Normal flora of vagina so exposed during birth

Question 7

What are the virulence factor of Strepto pyogenes ?

Answer 7

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

Question 8

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

Answer 8

• Inhibits phagocytosis by neutrophils and macrophages

- Because similar to human Hyaluronate in CT

Question 9

What is M protein and what is its role ?

Answer 9

• long chain of peptides sticking out of bacteria

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

Question 10

What are the actions of Streptolysins ?

Answer 10

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

Question 11

What is the role of streptokinase ?

Answer 11

Convert plasminogen in plasmin to dissolve clots

Question 12

What do Streptococcal pyrogenic exotoxins do ? SPE

Answer 12

• cleaves IgG bound to group A strep

- Activate T cell response : SUPERATIGENIC :inflammation

Question 13

What are the criteria of Streptococcal toxic shock syndrome ?

Answer 13

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

Question 14

What causes Strepto toxic shock ? (Steps)

Answer 14

• 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