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Dermatology > Virulence factors > Flashcards

Virulence factors Flashcards

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Dermatology Board Prep flashcards
1
Q

Describe the pathogenesis of infection?

A

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

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2
Q

What is virulence?

A

The capacity of a microbe to cause damage to the host

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3
Q

What are the virulence factors? What are their functions?

A

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

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4
Q

What does toxinosis mean?

A

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

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5
Q

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

A

It can colonise and infect several different areas of the body

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6
Q

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

A 
Fibrinogen binding (most common)
Collagen binding (less common)
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7
Q

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

A

Bone and joint

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8
Q

What main impedins do s.aureus posses?

A

Superantigens

Panton-Valentine Leukocidin (PVL)

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9
Q

What does PVL do?

A

Specifically targets and destroys leukocytes

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10
Q

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

A

True

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11
Q

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

A

Necrotising pneumonitis
Severe & contagious skin infections

PVL and alpha-toxin

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12
Q

PVL is an integrated bacteriophage. T/F

A

True

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13
Q

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

A

True

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14
Q

Describe the development of (untreated) necrotising pneumonia

A

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

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15
Q

Is necrotising pneumonia rapidly progressing?

A

Yes

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16
Q

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

A

Toxic shock syndrome toxin-1. A superantigen

17
Q

How do superantigens work?

A

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

18
Q

What is the diagnostic criteria for toxic shock syndrome?

A

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

19
Q

How quickly can toxic shock syndrome kill you?

A

3-4 hours

20
Q

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

A

Strep. pyogenes

21
Q

How are the strep. pyogenes classified?

A

By surface antigen (lancefield system)

22
Q

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

A

Impetigo
Cellulitis (erysipelas)
Necrotising fasciitis

23
Q

Describe streptococci pyrogenes

A

Gram positive cocci in chains

Catalase negative & beta-haemolytic

24
Q

What is the Lancefield system?

A

The serotypic of bacterial cell wall carbohydrate

25
Q

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

A

M protein

26
Q

What are the main adhesins that strep.pyrogenes possesses?

A 
Hyaluronic acid (capsule)
CD44 positive keratinocytes
27
Q

What is the benefit of a hyaluronic acid capsule?

A

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

28
Q

What are some diseases caused by group A strep?

A

Impetigo, cellulitis, erysipelas

29
Q

Where is impetigo situated within the skin?

A

The keratin layer

30
Q

What is cellulitis?

A

A skin infection involving the dermis and subcutaneous fat

31
Q

Is cellulitis associated with necrosis?

A

No

32
Q

What is erysipelas?

A

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

33
Q

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

A

Streptolysin S. By targeting leukocytes

34
Q

What diseases are streptococci pyrogenes responsible for?

A

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

35
Q

What is a pyrogen?

A

A substance which induces fever

36
Q

What toxins cause toxic shock like syndrome?

A

Pyrogenic exotoxins

37
Q

What is the progression of toxic shock like syndrome?

A

Hypotension > multi-organ failure

38
Q

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

A

S.aureus - localised infection

S.pyrogenes - invasive disease & bacteraemia

39
Q

Where is s.pyrogenes normally found?

A

Within the pharynx & adherent to skin

Dermatology (26 decks)

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