Virulence factors

Question 1

Describe the pathogenesis of infection?

Answer 1

Reservoir of pathogens > contact to host > adherence > colonisation > invasion > evade host defences > multiplication > completion of life cycle > exit from host > release & spread

Question 2

What is virulence?

Answer 2

The capacity of a microbe to cause damage to the host

Question 3

What are the virulence factors? What are their functions?

Answer 3

Adhesin - enables organism to bind to the host
Invasin - enables organism to invade host tissues
Impedin - enables the organism to avoid host defence mechanisms
Aggressin - causes damage to host directly
Modulin - induces damage to the host indirectly

Question 4

What does toxinosis mean?

Answer 4

Pathogenesis caused by bacterial toxin alone (not necessarily involving a bacterial infection)

Question 5

What gives an indication that s.aureus has many virulence factors?

Answer 5

It can colonise and infect several different areas of the body

Question 6

What are the two main adhesins that s.aureus possesses?

Answer 6

Fibrinogen binding (most common)
Collagen binding (less common)

Question 7

Which type of infections are common to s.aureus with collagen binding virulence factors?

Answer 7

Bone and joint

Question 8

What main impedins do s.aureus posses?

Answer 8

Superantigens

Panton-Valentine Leukocidin (PVL)

Question 9

What does PVL do?

Answer 9

Specifically targets and destroys leukocytes

Question 10

The presence of PVL in s.aureus is typically linked with very severe skin infections. T/F

Answer 10

True

Question 11

CA-MRSA is responsible for which types of infection? What impedins give it this virulence?

Answer 11

Necrotising pneumonitis
Severe & contagious skin infections

PVL and alpha-toxin

Question 12

PVL is an integrated bacteriophage. T/F

Answer 12

True

Question 13

On the whole, more virulent toxins are found in the community than in the hospital environment. T/F

Answer 13

True

Question 14

Describe the development of (untreated) necrotising pneumonia

Answer 14

Influenza-like syndrome > necrotising haemorrhagic pneumonia > acute respiratory distress > deterioration in pulmonary function > refractory hypoxamenia > multi-organ failure

Question 15

Is necrotising pneumonia rapidly progressing?

Answer 15

Yes

Question 16

What does TSST-1 stand for? What is it an example of?

Answer 16

Toxic shock syndrome toxin-1. A superantigen

Question 17

How do superantigens work?

Answer 17

They antigens are not processed by neutrophils and instead bind directly to MHC II complex causing the activation of T cells and inappropriate immune response

Question 18

What is the diagnostic criteria for toxic shock syndrome?

Answer 18

Fever >39
Diffuse macular rash & desquamation
Hypotension 3 organ systems involved

Question 19

How quickly can toxic shock syndrome kill you?

Answer 19

3-4 hours

Question 20

What is the most common cause of a bacterial sore throat?

Answer 20

Strep. pyogenes

Question 21

How are the strep. pyogenes classified?

Answer 21

By surface antigen (lancefield system)

Question 22

What skin infections are strep. pyogenes most commonly responsible for?

Answer 22

Impetigo
Cellulitis (erysipelas)
Necrotising fasciitis

Question 23

Describe streptococci pyrogenes

Answer 23

Gram positive cocci in chains

Catalase negative & beta-haemolytic

Question 24

What is the Lancefield system?

Answer 24

The serotypic of bacterial cell wall carbohydrate

Question 25

Which protein is useful for identifying different subtypes of strep.pyrogenes?

Answer 25

M protein

Question 26

What are the main adhesins that strep.pyrogenes possesses?

Answer 26

``` Hyaluronic acid (capsule) CD44 positive keratinocytes ```

Question 27

What is the benefit of a hyaluronic acid capsule?

Answer 27

It reduces phagocytosis (therefore increasing the virulence of the bacteria)

Question 28

What are some diseases caused by group A strep?

Answer 28

Impetigo, cellulitis, erysipelas

Question 29

Where is impetigo situated within the skin?

Answer 29

The keratin layer

Question 30

What is cellulitis?

Answer 30

A skin infection involving the dermis and subcutaneous fat

Question 31

Is cellulitis associated with necrosis?

Answer 31

No

Question 32

What is erysipelas?

Answer 32

A skin infection found more superficially than cellulitis and associated with fever, rigours and nausea

Question 33

What is the main virulence factor responsible for tissue destruction in streptococci pyrogenes? How does it destroy tissues?

Answer 33

Streptolysin S. By targeting leukocytes

Question 34

What diseases are streptococci pyrogenes responsible for?

Answer 34

Cellulitis (impetigo), necrotising faciitis and toxic shock like syndrome (TSLS)

Question 35

What is a pyrogen?

Answer 35

A substance which induces fever

Question 36

What toxins cause toxic shock like syndrome?

Answer 36

Pyrogenic exotoxins

Question 37

What is the progression of toxic shock like syndrome?

Answer 37

Hypotension > multi-organ failure

Question 38

What is the difference between s.aureus and s.pyrogenes in terms of infection spread?

Answer 38

S.aureus - localised infection | S.pyrogenes - invasive disease & bacteraemia

Question 39

Where is s.pyrogenes normally found?

Answer 39

Within the pharynx & adherent to skin