Bacterial pathogenesis - virulence factors and host damage Flashcards
What is virulence?
The relative capacity for a pathogen to cause damage in a host
What is virulence factor?
Components of a pathogen that determine its virulence
Which factors determine a bacterium’s ability to cause infections and disease?
Structural components
- adherence factors
- motility
Host defence evasions
- antiphagocytic factors/strategies
- anticomplement factors/strategies
Gene expression
- invasion factors
- endotoxin production
- exotoxin production
Which methods do bacteria use to evade host denfence systems?
Use of capsules => more difficult to phagocytose
e.g. Pneumococcus
Detection avoidance
Damage/interferrence of immune cells
Resistance to immune cells
How can bacterial pathogens cause direct damage?
Harmful metabolites
Degradative enymes and toxins
Growth in host cells
How can bacterial pathogens cause indirect damage?
Inflammation and the immune response
Using host’s nutrients, e.g. siderophores
What are the two types of bacterial toxins?
Exotoxins
Endotoxins
Describe the characteristics of exotoxins
Actively produce and secreted by G +ve and -ve bacteria
High molecular weight polypeptides
Relatively unstable (good for host)
Highly toxic (bad for host)
Synthesised form plasmids (short piece of DNA)
Describe the characteristics of endotoxins
Lipopolysaccharide complex synthesised from nucleoid found in G -ve walls
Released on bacterial death
Relatively stable
Weakly toxic - don’t directly damage
What effects does lipopolysaccharide have on host?
Cause various effects such as fever and shock by causing inflamamtory response
- can be beneficial
- can be dangerous if excessive
Is LPS the only endotoxin?
No but often endotoxin is defined as LPS
What are exotoxins four main mechanisms of action?
Cell/tissue degrading enzymes e.g. proteases
Alters signalling pathways
Neurotoxins - acts on NS
Superantigens - non specific T cell activation
What are type 1 toxins?
Membrane acting toxins
- intefere with host cell transduction pathways, from outside the target cell
What are type 2 toxins?
Membrane-disrupting toxins (2 types)
- pore forming = generate channel and disrupt membrane
- enzymatic = destroy membrane phospholipid integrity
What are type 3 toxins?
Intracellularly acting toxins
- Interfere with host cell from inside the cell
- Often specific activity
