Virulence Factors Flashcards
1
Q
Koch’s postulates
A
- The bacterium must be found in all people with the disease in the correct location
- The bacterium should be isolated from the infected site and maintained in pure culture
- The pure culture should be capable of causing the disease
- The same bacterium should be isolated from the intentionally infected host.
2
Q
Virulence
A
Ability of a bacterium to cause disease
3
Q
Virulence Factor
A
A bacterial product or structure or strategy that contributes to virulence
4
Q
Molecular Koch’s Postulates
A
- Gene present in virulent strain should be absent or inactive in avirulent strains
- Disrupting the gene in a virulent strain should diminish virulence or introducing the egen to an avirulent strain should make it virulent
- Gnese should be expressed during infection
- Antibodies to gene product should be protective
5
Q
Example of afimbrial adhesion
A
Strep pyogenes has an adhesion protein F which binds to fibronectin - casting throat and wound infections
6
Q
Explain evading complement
A
- Attachment of sialic acid to the LPS O antigen alters LPS which is the main target for complement
- bacteria produce proteins that bind to antibodies (e.g. Protein A by S.aureus) which bind to Fc portion and cause neutralisation
- Loss of capsule - prevents opsonisation
7
Q
Exotoxin
A
- produced inside the cell (mostly gram +) and are secreted following lysis into surrounding medium
- can be cytotoxic or specific
- e.g. Chlorea toxin
8
Q
Endotoxin
A
- part of the outer portion of the cell wall of gram - bacteria (LPS)
- liberated when cell dies or cell wall breaks apart
- all gram - have LPS thus all have endotoxin in outer leaflet of outer membrane
9
Q
Toxic component of LPS
A
Lipid A
10
Q
Function of LPS
A
- LPS binds to LPS -binding protein which triggers cytokine release which can lead to a cascade of event characterised as shock
- shock can lead to MOSF
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11
Q
What are the categories of exotoxins?
A
- A-B toxin (combo of A and B subunits; can be complex or simple)
- Membrane disrupting (pore-forming or membrane damaging)
- Superantigen (responsible for toxic shock)
12
Q
Explain simple A-B toxins
A
- produced as a single protein from a single gene
- cleaved by host protease into A and B subunits
- linked together by S-S bridge
- A: active subunit
- B: binding subunit - binds to target cell and delivers A subunit
13
Q
Explain complex A-B toxins
A
- 2 genes
- A subunit proteolytically cleaved into A1 and A2 - held together by disulphide bridge
- A1 subunit contains toxic activity
- 1 A subunit: 5 B subunits
- A2 subunit interacts with B subunits - delivers A1 to target cells
14
Q
Types of membrane disrupting toxins
A
- Pore-forming - binds to receptor, inserts into membrane forming a pore, cell content leak out and cell dies (e.g. BT toxin)
- Phospholipases - cleaves phospholipid heads which destablises the membrane (e.g. Phospholipase A2)
15
Q
Bioassay used to identify membrane-disrupting toxins
A
Hemolysins - lyse RBCs
