Other: Molecular Basis of Bacterial Virulence Flashcards
Which toxinoses of S. aureus is associated with staphylococcal food poisoning?
Enterotoxin SeA SeB and SeC
What is the function of M protein in the capsule of GAS?
Allows it to bind to multiple body surfaces and interferes with immune response
How do adhesions act as a virulence factor for staphylococci?
Fibrinogen-binding (CIfA CIfB) and fibronectin-binding (FnbpA FNbpB) proteins are an important part of colonisation
What is Lancefield grouping?
System of classification that classifies streptococci based on the carbohydrate composition of bacterial antigens found on their cell walls (Groups A-G)
How does coagulase help S. aureus to evade host defences?
Protein enzyme tightly bound to the surface of S. aureus which can coat its surface with fibrin upon contact with blood → protects against phagocytosis
What is Panton-Valentine Leukocidin?
Specific secreted proteins that form one functional complex that attacks white blood cells
Associated with severe skin infections and necrotising pneumonia
Define ⍺-haemolysis
Partial haemolysis - green tinge to colony
Name the superantigen which is the most common cause of toxic shock and the bacterium it is associated with
TSST-1 S. aureus
How does the capsule help S. aureus to evade host defences?
Protects it against phagocytosis
Which genus of gram-positive bacteria is classified using haemolysis?
Streptococci
Define 𝛾-haemolysis
No haemolysis
How does protein A help S. aureus to evade host defences?
Impairs phagocytosis by binding to the Fc portion of antibodies, rendering them inaccessible to the opsonins
Name a coagulase-positive staphylococci that colonises the skin and mucous membranes (20-60%)
Staph. aureus
Which streptococci are ⍺-haemolytic?
Step. pneumonae, viridans streptococci, most oral streptococci
What is streptolysin?
Streptococcal haemolytic exotoxin - causes tissue damage and ulcers
Types include SLO and SLS - SLS is responsible for β-haemolysis
Define β-haemolysis
Complete haemolysis
Which bacteria is the major cause of infections associated with prosthetic devices and catheters?
Staph. epidermis
How do iGAS cause necrotising fasciitis?
iGAS strains penetrate mucous membrane and develop in lesion
Severe infection with rapid destruction of connective tissue develops
Leads to toxic shock (with or without TSLS superantigen)
Define Group A Streptococci (GAS)
Strep. pyrogenes (mostly) - β-haemolytic streptococci
Associated with throat infections (strep throat) and skin infections (impetigo, cellulitis, necrotising fasciitis)
Define necrotising pneumonia
Severe complication of quite mild infections due to disruption of immune cells
S. aureus necrotising pneumonia is due to the actions of PVL
Which streptococci are β-haemolytic?
S. pyogenes and angionosus group of oral streptococci
Define virulence factor
The molecular/genetic basis of pathogenesis that characterises species, subspecies and strains
Outline how TSST-1 causes toxic shock syndrome
Antigen binds directly to MHCII complex causing the activation of 1 in 5 T cells
This results in a massive release of cytokines and inappropriate immune response
Name a coagulase-negative staphlococci that colonises the skin and mucous membranes (100%)
Staph. epidermis
Which streptococci are 𝛾-haemolytic?
Enterococci (Lancefield Group D)
Define toxinoses
Discrete disease associated with single protein component, a toxin or exotoxin (not the endotoxin)
How are Group A streptococci further classified?
Divided according to M protein antigens (coded by emm gene)
Which M protein antigens are associated with severe invasive disease (iGAS)?
M3 and M18
Which emm gene is associated with GAS epidemics?
emm89
