Bacterial Immune Evasion Flashcards
(52 cards)
what is Staphylococcus aureus
Gram positive bacteria that is commensal and lives harmlessly in nose.
Is able to cause minor skin infections to severe and life threatening diseases.
what are the 2 groups S. Aureus can be divide into?
- localised pyogenic diseases characterised by tissue destruction, mediated by hydrolytic enzymes and cytotoxins
- diseases mediated by toxins that function as super antigens producing systemic diseases
What is a pyogenic disease?
one that causes pus to be produced
What are pyogenic diseases mediated by
hydrolytic enzymes and toxins
What are systemic diseases mediated by?
Toxins
what is S. Pyogenes
gram + bacteria , lives harmlessly in throat/
what 3 groups can S. Pyogenes be split into?
- localised diseases characterised by tissue destruction e.g pharyngitis
- diseases mediated by toxins that function as super antigens producing systemic diseases
- post- infection sequelae
How is chemotaxis inhibited by S. Aureus?
- S.Aureus releases CHIPs
- binds to C5aR
- prevents binding of C5a
- hence, neutrophils not activated as no C5a binding
what are the three main methods of evading antibody opsonisation?
- Use of capsules to hide bacteria
2.Use of surface proteins to prevent detection - Use of proteases to degrade antibodies
How is the expression of a capsule useful in bacterial immune evasion?
Use of a polysaccharide capsule helps to hide the antigenic structures of bacteria from adaptive immune components
How does S. aureus use surface proteins to prevent detection?
S. aureus has protein A on its surface (Spa).
Spa proteins bind to antibodies via their Fc (constant) region not their Fab (variable) region.
This prevents normal opsonisation, and therefore neutrophils cannot detect S. aureus.
How does S.pygones use surface proteins to prevent detection?
they have M surface proteins
these proteins bind to antibodies via their Fc (constant) region not their Fab (variable) region.
This prevents normal opsonisation, and therefore neutrophils cannot detect S.pyogenes
How can bacteria expressing proteases affect antibody opsonisation?
proteases cleave antibodies into many non-functional forms
This prevents IgGs binding to bacterial surface and performing their function.
what is another antibody opsonisation evasion strategy and why is it useful?
bacteria have antigenic variation.
Switching expression of antigens means antibodies that recognise the first surface structure are unable to recognise those bacteria now
what is complement opsonisation?
Complement system is composed of large number of proteins that react with one another to opsonise pathogens or to directly kill them by membrane attack complex (MAC) formation
What are the four key steps in the complement cascade?
- Initiation
- Formation of C3 convertase
- formation of C5 convertase
- MAC formation
What are the 4 ways in which bacteria specificallu S. Aureus evades complement opsonisation?
1.cleave complement factors such as C3
2. Inhibit C3/C5 convertases
3. recruit negative regulators
4. bind complement factors and prevent their processing
What protein binds to C3bBb and prevents the formation of C3 convertase and C5 convertase?
SCIN
How does S. aureus inhibit complement convertase?
Produces SCIN protein which binds to C3bBb and inhibits the formation of C3 convertase and C5 convertase
what are the 3 initiation pathways that result in C3 converts formation?
- classical pathway
- lectin pathway
- alternative pathway
What does the deposition of C3b on the microbe allow? d
The detected of the microbe by certain receptors on neutrophils / phagocytes
What is the name of a protein which degrades antibodies by cleavage?
IdeS - separates the Fc and Fab region
Why is S. aureus a common cause of food poisoning?
Because they are able to grow in high salt concentrations
What two enzymes does S. aureus have?
Coagulase and catalase
