I: Streptococci (Pyogenes Focus)

Question 1

What classification of organism is streptococci?

Answer 1

Gram positive cocci (string appearance)

Question 2

How can you tell the difference between alpha, beta and gamma streptococci?

Answer 2

Alpha: partial haemolysis
Beta: complete haemolysis
Gamma: no haemolysis

Question 3

Describe what is meant by a somatic virulence factor.

Answer 3

The agents used by the pathogen to evade the immune system that are an integral part of the organism.

Question 4

Describe what is meant by an endotoxin virulence factor.

Answer 4

The agents used by the pathogen to evade the immune system that are released by the pathogen.

Question 5

Name some virulence factors of streptococcus pyogenes.

Answer 5

• Hyaluronic acid capsule
• M protein
• Adhesins
• Streptolysins O and S
• Dnases A, B, C and D
• Hyaluronidase
• Streptokinease
• Pyrogenic exotoxins

Question 6

How does the hyaluronic acid capsule of streptococcus pyogenes act as a virulence factor?

Answer 6

• Inhibits phagocytosis

- Poor immune reaction to the capsule as it is similar to that of human connective tissue

Question 7

How does the M proteins of streptococcus pyogenes act as a virulence factor?

Answer 7

• Resists phagocytosis by activating alternative complement athwart on bacterial surface

Question 8

How do the adhesins found on streptococcus pyogenes act as a virulence factor?

Answer 8

Aids adhesion to allow colonisation

Question 9

How does streptolysins O and S of streptococcus pyogenes act as a virulence factor?

Answer 9

Lysis of erythrocytes, neutrophils, platelets.

Question 10

How do Dnases A, B, C and D found within streptococcus pyogenes act as a virulence factor?

Answer 10

Degradation of DNA

Question 11

How does hyaluronidase found within streptococcus pyogenes act as a virulence factor?

Answer 11

Degredation of hyaluronic acid in connective tissue

Question 12

How do streptokinase found within streptococcus pyogenes act as a virulence factor?

Answer 12

Dissolution of clots through conversion of plasminogen into plasmin.

Question 13

How do pyrogenic exotoxins found within streptococcus pyogenes act as a virulence factor?

Answer 13

Cleaves Ig G bound to group A strep.

Question 14

Describe the main clinical features of streptococcal pharyngitis.

Answer 14

• Abrupt onset sore throat
• Fever
• Headache
• Lymphoid hyperplasia

Question 15

How is strep pharyngitis spread?

Answer 15

• Droplets

- Associated with over crowding

Question 16

Describe the main clinical features of scarlet fever.

Answer 16

• High fever
• Sepsis
• Arthritis
• Jaundice

Question 17

Name 3 complications of streptococcal pharyngitis.

Answer 17

• Scarlet fever
• Acute rheumatic fever
• Acute post-streptococcal glomerulonephritis

Question 18

Name 4 skin infections that result from streptococcus pyogenesand where they affect.

Answer 18

• Impetigo (epithelia infection)
• Erysipelas (dermis infection)
• Cellulitis (skin and subcutaneous tissue infection)
• Necrotising fasciitis (deeper subcutaneous tissue and fascia)

Question 19

What is streptococcal toxic shock syndrome?

Answer 19

A deep tissue infection with group A strep pyogenes