17 - Bacterial Pathogenesis Flashcards
Bacteria which commonly have afimbrial adhesins
G- bacteria (as are often inserted in outer cell membrane)
Proportion of microbiome that is in large intestine
~70%
Protein that ETEC uses to bind to human intestinal epithelium
CS3
Experiment looking at ETEC virulence in piglets
Without K88 adhesin, there was no ETEC adhesion to intestinal wall, an no pathogenesis, even in E coli that were toxin+ (no diarrhoea)
How can piglets be immunised?
Immunise sow, when piglets suckle milk get sow’s IgA
Travelan
Antibodies against ETEC.
Treats traveller’s diarrhoea
Where do yersinia enter intestinal wall?
Through M cells
Which protein does yersinia use to enter M cells?
Invasin
What does yersinia invasin bind to?
Integrin on M cell
What are pyogenic bacteria?
Pathogenic bacteria that evade phagocytosis, resulting in pus formation
Example of bacterium which produces leukocidins
S pyogenes, S aureus
Example of a bacterium that produces an anti-inflammatory
Choleratoxin is an anti-inflammatory agent
Number of S. pneumoniae capsular antigens
Around 90
Is there any cross-reactivity between Ig against S. pyogenes capsules?
No
Adult pneumococcal vaccine
23 most-common S. pyogenes capsular antigens
Children’s’ pneumococcal vaccine
13 most-common S. pyogenes capsular antigens
How can capsulated bacteria be opsonised?
Anti-capsular antigen Ig binds, and complement binds to Ig Fc region
Most important type of meningococcus worldwide
Type A
Most important type of meningococcus in Australia
Type B
Example of a bacterium with an non-antigenic capsule
Meningococcus type B
Stages of phagocytosis 1) 2) 3) 4) 5) 6)
1) Chemotaxis
2) Attachment
3) Metabolic burst
4) Ingestion
5) Phagolysosome formation
6) Destruction
Some strategies used by bacteria to evade destruction by phagocytes 1) 2) 3) 4)
1) Inhibit respiratory burst
2) Prevent phagolysosome formation
3) Escape from phagocytic vacuole
4) Resist bactericidal systems
C’ pathway activated by LPS
Alternative pathway
Non-professional phagocytes
Cells that need to be induced to plagocytose.
EG: With SIP proteins
Substrate of lysozyme
Beta1-4 linkage in peptidoglycan
Why are newborn babies a risk group for tetanus infection?
Some cultures cover necrotising umbilical cord with cow dung. C tetani lives in cow faeces (and faeces of other animals), colonises necrotising tissue.
Only way that you can get anti-tetanustoxin Ig
Immunisation. The amount of tetanospasmin required for Ig production in a natural infection would kill you.
How can replicating bacteria release endotoxin?
Some G- bacteria release bits of cell wall
Pyrogen free
Autoclaving won’t inactivate endotoxin. Pyrogen free means endotoxin has been removed
Heat resistance of endotoxin
High
Ways to overcome adaptive immune system 1) 2) 3) 4)
1) Direct immunosuppression
2) Expression of weak antigens
3) Antigenic diversity
4) Antigen modification
Chemical nature of exotoxin
Protein
Chemical nature of endotoxin
LPS
Antigenicity of exotoxin versus endotoxin
Exotoxin highly antigenic. Endotoxin variable
Specificity of exotoxin versus endotoxin
Exotoxin very specific. Endotoxin non-specific (as induces immune response)
Broad division of bacterial exotoxin modes of action
1) Cytotoxic (inhibitory), EG leukocidins
2) Cytotonic (excitatory), EG choleratoxin
Examples of intracellularly acting, cytotoxic exotoxins
1)
2)
1) Diphtheriatoxin
2) Shigatoxin
Example of a simple exotoxin
Heat-stable enterotoxin
Shigatoxin receptor
gb3
SHigatoxin mechanism
A1 subunit modifies 28S rRNA of 60S ribosomal subunit, prevents protein synthesis
