Bacterial Virulence

Question 1

Define virulence

Answer 1

The capacity of a microbe to cause damage to the host

Question 2

What does Adhesin do?

Answer 2

Enables binding of the organism to host tissue

Question 3

What does Invasin do?

Answer 3

Enables the organism to invade a host/cell tissue

Question 4

What does Impedin do?

Answer 4

Enables the organism to avoid host defense mechanisms

Question 5

What does Aggressin do?

Answer 5

Causes damage to the host directly

Question 6

What does Modulin do?

Answer 6

Induces damage to the host indirectly

Question 7

Describe how adhesins work?

Answer 7

Extracellular matrix molecules are present on epithelial, endothelial surfaces as well as a component of blood clots

Question 8

What factors aid in the evasion of host defences?

Answer 8

Protein A, proteases, superantigens, lipases, phospholipases, esterase, gamma toxin, alpha toxin & PVL, coagulase and capsule producing capsular poluysaccharides (Mucoid/Microcapsule)

Question 9

What is Panton-Valentine Leukocidin (PVL)?

Answer 9

PVL bicomponent toxin produced by strains of Staph aureus. Specific toxicity for Leukocytes, present in 1-2% strains. Associated with severe skin infection.

Question 10

Describe necrotizing pneumonia

Answer 10

Preceding influenza like syndrome. Haemorrhagic. Rapid progression, acute resp distress, deterioration in pulmonary function, refractory hypoxaemia. Multi-organ failure despite Abiot therapy

Question 11

What do superantigens do?

Answer 11

Activate 1 in 5 T cells (normal Ag 1:10000). Massive release of cytokines & inappropriate immune response.

Question 12

What is superantigen TSST-1 particularly associated with?

Answer 12

Toxic shock

Question 13

Describe the diagnostic criteria for necrotizing pneumonia?

Answer 13

Fever, diffuse macular rash and desquamation, hypotension, >=3 organ systems involved

Question 14

What skin infections can be caused by Strep pyogenes?

Answer 14

Impetigo, cellulitis (erysipelas), necrotizing fasciitis

Question 15

Which classification system is used for strep pyogenes?

Answer 15

Lancefield

Question 16

What substances cause tissue/cell destruction?

Answer 16

Hemolysins, streptolysin S (SLS)- pore forming cytolysin. Toxic to PMN, organelles, platelets.

Question 17

Describe Toxic shock like syndrome (TSLS)

Answer 17

Pyrogenic exotoxin(s)- complication of invasive infection, 30% mortality, hours to days, hypotension to organ failure

Question 18

What superantigens are involved in menstrual and non menstrual S. aureus infection?

Answer 18

Menstrual- TSST-1. Non menstrual- SEB/SEC

Question 19

What toxins are the most commonly produced by S. pyogenes?

Answer 19

SpeA and SpeC

Question 20

Where is S. pyogenes normally found?

Answer 20

Pharynx

Question 21

Name some virulence factors

Answer 21

Capsule, fibrinogen binding protein, haemolysins alpha, beta, theta, gamma, coagulase, fibrinolysin, leukocidin (PVL), hyaluronidase, protein A, epidermolytic toxins A & B, enterotoxin, TSST-1

Question 22

What is a capsule’s mode of action?

Answer 22

Antiphagocytic

Question 23

What is Fibrinogen Binding protein’s mode of action?

Answer 23

Adhesin

Question 24

What are Haemolysins alpha, beta, theta and gamma’s mode of action?

Answer 24

Cytolytic (erythrocytes)

Question 25

What is Coagulase’s mode of action?

Answer 25

Clots plasma

Question 26

What is Fibrinolysin’s mode of action?

Answer 26

Digests fibrin

Question 27

What is Leukocidin (PVL) mode of action?

Answer 27

Kills leukocytes

Question 28

What is Hyaluronidase mode of action?

Answer 28

Hyaluronic acid (ECM)

Question 29

What is Protein A’s mode of action?

Answer 29

Antiphagocytic

Question 30

What is Epidermolytic Toxins A & B mode of action?

Answer 30

Epidermal splitting/exfoliation

Question 31

What is Enterotoxin’s mode of action?

Answer 31

V & D

Question 32

What is TSST-1’s mode of action?

Answer 32

Shock, rash, desquamation