Staph Aureus & Strep Pyogenes Virulence Flashcards
What is a virulence factor
Component of a pathogen that influences its ability to cause disease/pathology (not necessarily essential)
State the 5 sub groups of virulence factors
Adhesions, Invasins, Impedins, aggressins, modulins
What are adhesions
They enable binding of organism to host tissue
What are invasins
Enable organisms to invade a host cell/ tissue
What are impedins
Enable organisms to avoid host defence mechanisms
What are aggressins
Cause damage to the host directly
What are modulins
Induce damage to the host indirectly
Name some conditions that can be caused by staph aureus
Superficial, dermatological
- Impetigo, abscesses, folliculitis, carbuncle
Systemic, life threatening
- Endocarditis, pneumonia, osteomyelitis, MRSA bacteraemia
Toxinoses
- Toxic shock, scalded skin syndrome, food poisoning
What is TSST-1
- A toxin produced by staph aureus
- Is associated with toxic shock
- Causes massive release of cytokines & inappropriate (excessive) immune response
How is toxic shock syndrome diagnosed
- Fever
- Diffuse macular erythroderma
- Hypotension
- > 3 organ systems involved in
What does coagulase do
Coagulase binds to prothrombin (staphylothrombin)
Staphylothrombin converts fibrinogen to fibrin
This promotes clot formation
What protein allow staph aureus to evade the immune system
Protein A (binds to antibodies incorrectly, avoiding detection)
What is Panton-Valentine Leukocidin
- A bicomponent toxin released by staph aureus
- Is toxic for leukocytes & so minimises immune response
- Is associated with severe skin infections (furunculosis) & necrotising pneumonia
Summarise the main toxins associated with staph aureus
What type of strep is strep pyogenes
Group A streptococci
What conditions are commonly caused by strep pyogenes
Upper respiratory tract infections (scarlet fever)
Superficial, contagious skin infections (Impetigo)
Invasive skin infections (cellulitis, necrotising fasciitis)
Rheumatic fever
Glomerularnephritis
Surface proteins e.g. M protein - determines where colonises (skin or throat)
Superantigens e.g. those involved in scarlet fever - Causes fever, damages peripheral blood vessels
Haemolysin/ SLS - impetigo -> cellulitis -> necrotising fasciitis
What proteins of strep pyogenes are linked to more aggressive, invasive diseases
SLS
