Virulence factors Flashcards
Describe the pathogenesis of infection?
Reservoir of pathogens > contact to host > adherence > colonisation > invasion > evade host defences > multiplication > completion of life cycle > exit from host > release & spread
What is virulence?
The capacity of a microbe to cause damage to the host
What are the virulence factors? What are their functions?
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
What does toxinosis mean?
Pathogenesis caused by bacterial toxin alone (not necessarily involving a bacterial infection)
What gives an indication that s.aureus has many virulence factors?
It can colonise and infect several different areas of the body
What are the two main adhesins that s.aureus possesses?
Fibrinogen binding (most common) Collagen binding (less common)
Which type of infections are common to s.aureus with collagen binding virulence factors?
Bone and joint
What main impedins do s.aureus posses?
Superantigens
Panton-Valentine Leukocidin (PVL)
What does PVL do?
Specifically targets and destroys leukocytes
The presence of PVL in s.aureus is typically linked with very severe skin infections. T/F
True
CA-MRSA is responsible for which types of infection? What impedins give it this virulence?
Necrotising pneumonitis
Severe & contagious skin infections
PVL and alpha-toxin
PVL is an integrated bacteriophage. T/F
True
On the whole, more virulent toxins are found in the community than in the hospital environment. T/F
True
Describe the development of (untreated) necrotising pneumonia
Influenza-like syndrome > necrotising haemorrhagic pneumonia > acute respiratory distress > deterioration in pulmonary function > refractory hypoxamenia > multi-organ failure
Is necrotising pneumonia rapidly progressing?
Yes
What does TSST-1 stand for? What is it an example of?
Toxic shock syndrome toxin-1. A superantigen
How do superantigens work?
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
What is the diagnostic criteria for toxic shock syndrome?
Fever >39
Diffuse macular rash & desquamation
Hypotension 3 organ systems involved
How quickly can toxic shock syndrome kill you?
3-4 hours
What is the most common cause of a bacterial sore throat?
Strep. pyogenes
How are the strep. pyogenes classified?
By surface antigen (lancefield system)
What skin infections are strep. pyogenes most commonly responsible for?
Impetigo
Cellulitis (erysipelas)
Necrotising fasciitis
Describe streptococci pyrogenes
Gram positive cocci in chains
Catalase negative & beta-haemolytic
What is the Lancefield system?
The serotypic of bacterial cell wall carbohydrate
Which protein is useful for identifying different subtypes of strep.pyrogenes?
M protein
What are the main adhesins that strep.pyrogenes possesses?
Hyaluronic acid (capsule) CD44 positive keratinocytes
What is the benefit of a hyaluronic acid capsule?
It reduces phagocytosis (therefore increasing the virulence of the bacteria)
What are some diseases caused by group A strep?
Impetigo, cellulitis, erysipelas
Where is impetigo situated within the skin?
The keratin layer
What is cellulitis?
A skin infection involving the dermis and subcutaneous fat
Is cellulitis associated with necrosis?
No
What is erysipelas?
A skin infection found more superficially than cellulitis and associated with fever, rigours and nausea
What is the main virulence factor responsible for tissue destruction in streptococci pyrogenes? How does it destroy tissues?
Streptolysin S. By targeting leukocytes
What diseases are streptococci pyrogenes responsible for?
Cellulitis (impetigo), necrotising faciitis and toxic shock like syndrome (TSLS)
What is a pyrogen?
A substance which induces fever
What toxins cause toxic shock like syndrome?
Pyrogenic exotoxins
What is the progression of toxic shock like syndrome?
Hypotension > multi-organ failure
What is the difference between s.aureus and s.pyrogenes in terms of infection spread?
S.aureus - localised infection
S.pyrogenes - invasive disease & bacteraemia
Where is s.pyrogenes normally found?
Within the pharynx & adherent to skin
