Bacterial Virulence Flashcards
Define virulence
The capacity of a microbe to cause damage to the host
What does Adhesin do?
Enables binding of the organism to host tissue
What does Invasin do?
Enables the organism to invade a host/cell tissue
What does Impedin do?
Enables the organism to avoid host defense mechanisms
What does Aggressin do?
Causes damage to the host directly
What does Modulin do?
Induces damage to the host indirectly
Describe how adhesins work?
Extracellular matrix molecules are present on epithelial, endothelial surfaces as well as a component of blood clots
What factors aid in the evasion of host defences?
Protein A, proteases, superantigens, lipases, phospholipases, esterase, gamma toxin, alpha toxin & PVL, coagulase and capsule producing capsular poluysaccharides (Mucoid/Microcapsule)
What is Panton-Valentine Leukocidin (PVL)?
PVL bicomponent toxin produced by strains of Staph aureus. Specific toxicity for Leukocytes, present in 1-2% strains. Associated with severe skin infection.
Describe necrotizing pneumonia
Preceding influenza like syndrome. Haemorrhagic. Rapid progression, acute resp distress, deterioration in pulmonary function, refractory hypoxaemia. Multi-organ failure despite Abiot therapy
What do superantigens do?
Activate 1 in 5 T cells (normal Ag 1:10000). Massive release of cytokines & inappropriate immune response.
What is superantigen TSST-1 particularly associated with?
Toxic shock
Describe the diagnostic criteria for necrotizing pneumonia?
Fever, diffuse macular rash and desquamation, hypotension, >=3 organ systems involved
What skin infections can be caused by Strep pyogenes?
Impetigo, cellulitis (erysipelas), necrotizing fasciitis
Which classification system is used for strep pyogenes?
Lancefield
What substances cause tissue/cell destruction?
Hemolysins, streptolysin S (SLS)- pore forming cytolysin. Toxic to PMN, organelles, platelets.
Describe Toxic shock like syndrome (TSLS)
Pyrogenic exotoxin(s)- complication of invasive infection, 30% mortality, hours to days, hypotension to organ failure
What superantigens are involved in menstrual and non menstrual S. aureus infection?
Menstrual- TSST-1. Non menstrual- SEB/SEC
What toxins are the most commonly produced by S. pyogenes?
SpeA and SpeC
Where is S. pyogenes normally found?
Pharynx
Name some virulence factors
Capsule, fibrinogen binding protein, haemolysins alpha, beta, theta, gamma, coagulase, fibrinolysin, leukocidin (PVL), hyaluronidase, protein A, epidermolytic toxins A & B, enterotoxin, TSST-1
What is a capsule’s mode of action?
Antiphagocytic
What is Fibrinogen Binding protein’s mode of action?
Adhesin
What are Haemolysins alpha, beta, theta and gamma’s mode of action?
Cytolytic (erythrocytes)
What is Coagulase’s mode of action?
Clots plasma
What is Fibrinolysin’s mode of action?
Digests fibrin
What is Leukocidin (PVL) mode of action?
Kills leukocytes
What is Hyaluronidase mode of action?
Hyaluronic acid (ECM)
What is Protein A’s mode of action?
Antiphagocytic
What is Epidermolytic Toxins A & B mode of action?
Epidermal splitting/exfoliation
What is Enterotoxin’s mode of action?
V & D
What is TSST-1’s mode of action?
Shock, rash, desquamation
