Lecture 9 - Bacterial Pathogenesis - Adherence, Colonisation Flashcards
What are the stages of bacterial pathogenesis? 1) 2) 3) 4) 5)
1) Enter the body
2) Colonise the host
3) Evade host defences
4) Multiply, disseminate in host
5) Cause damage to host
What is the advantage of Strep. pyogenes’ capsule?
Made of hyaluronic acid
Very similar to many host cell surfaces, therefore not readily detected by immune system
Feature of bacteria causing very persistent infection
Biofilm formation
How is a biofilm formed?
Bacteria aggregate, secrete ECM of protein, polysaccharides, DNA
How might a biofilm contribute to antibiotic resistance?
1)
2)
1) Bacteria in biofilm can become inert - antibiotics affect growing or dividing bacteria
2) Barrier between bacteria and antibiotic
Where can biofilms be frequently found? 1) 2) 3) 4) 5)
1) Implants
2) Catheters
3) Artificial heart valves
4) Teeth
5) Contact lenses
Which bacterium often colonises catheters?
Pseudomonas aeruginosa
Enterococcus
Stages of biofilm production 1) 2) 3) 4) 5)
1) Adhesion
2) Colonisation
3) Cell-cell adhesion
4) Proliferation
5) Maturation
Planktonic bacteria leave biofilm, adhere to another structure
Which bacteria most commonly cause biofilms on tonsils?
Staph. aureus
Haemophilus influenzae
Types of bacterial colonisation
1)
2)
3)
1) Loose association
2) Tight association
3) Invasion
Most accessible part of host cell
Glycocalyx
Function of b1 integrins
Attach cell cytoskeleton to extracellular matrix
Common bacterial target in GIT
M cells
Have much thinner layer of mucus covering them than other parts of GIT
What do bacterial adhesins normally target?
Polysaccharide structures
Example of host cell protein receptor often bound to by bacterial adhesins
Beta-1 integrin receptor
Two types of adhesins
1) Fimbrial adhesins (loose associations)
2) Afimbrial adhesins (outer membrane proteins)
Type of bacteria which most commonly have pili
Gram -
What do type I pili bind?
Mannose in glycoproteins
What do Pap pili do?
Bind Gal alpha(1-4)Gal in glycolipids
Requirements of Pap/Type I pili construction
Usher/chaperone system
Which bacterium often colonises catheters?
Pseudomonas aeruginosa
Enterococcus
Stages of biofilm production 1) 2) 3) 4) 5)
1) Adhesion
2) Colonisation
3) Cell-cell adhesion
4) Proliferation
5) Maturation
Planktonic bacteria leave biofilm, adhere to another structure
Which bacteria most commonly cause biofilms on tonsils?
Staph. aureus
Haemophilus influenzae
Types of bacterial colonisation
1)
2)
3)
1) Loose association
2) Tight association
3) Invasion
How does pilin get moved from cytoplasm to cell surface?
1)
2)
3)
1) Sec is a channel which brings pilin from cytoplasm to periplasmic space
2) Pilin needs to form correct disulphide bonds, find chaperone, or else is degraded
3) Chaperone/protein complex binds usher, usher brings pilin from periplasmic space to cell surface. PIlin is incorporated into pilus
Function of b1 integrins
Attach cell cytoskeleton to extracellular matrix
Common bacterial target in GIT
M cells
Have much thinner layer of mucus covering them than other parts of GIT
What do bacterial adhesins normally target?
Polysaccharide structures
Example of host cell protein receptor often bound to by bacterial adhesins
Beta-1 integrin receptor
Which pili use a type II secretion system?
Type IV pili
Type of bacteria which most commonly have pili
Gram -
What do type I pili bind?
Mannose in glycoproteins
What do Pap pili do?
Bind Gal alpha(1-4)Gal in glycolipids
Requirements of Pap/Type I pili construction
Usher/chaperone system
Function of usher protein
1) Usher binds chaperone/pilin complex in periplasmic space.
2) Pilin moved across cell membrane by usher, attached to pilus
Structure of pilus
Composite fibre made up of six structural proteins
Helical array of pilin
In pap and fim gene clusters, what is the function of major pilus subunit gene?
Pilin encoding
Intimin
1)
2)
1) 94kDa outer membrane protein
2) Afimbrial adhesin
How does pilin get moved from cytoplasm to cell surface?
1) Sec is a channel which brings pilin from cytoplasm to periplasmic space
2) Pilin needs to form correct disulphide bonds, find chaperone, or else is degraded
3) Chaperone/protein complex binds usher, usher brings pilin from periplasmic space to cell surface. PIlin is incorporated into pilus
Features of type IV pili 1) 2) 3) 4)
1) Don’t use usher/chaperone system of transport
2) Usually polar location
3) Can form bundles
4) Play a role in inter-bacterial interactions, host-cell mucosal surface adhesion, twitching motility
Relationship between Arp2/3, N-WASP and Nck
Nck joins Arp2/3 and N-WASP to actin
What is twitching motility?
1)
2)
3)
1) Different motility to runs and tumbles
2) Bacteria attach, retract pili to move
3) Leading rafts are forwardmost groups of bacteria
Which secretion system do type IV pili use?
Type II secretion system
Which pili use a type II secretion system?
Type IV pili
Is Bordatella pertussis G+ or G-?
Gram -
Example of bacterium that uses afimbrial adhesion
B. pertussis
Most important afimbrial adhesin in B. pertussis
Filamentous haemagglutinin
Features of filamentous haemagglutinin
1)
2)
1) 220kDa protein
2) Contains RGD motif - RGD motif found in human cells, binds fibronectin
3) Most important afimbrial adhesin in B. pertussis
Bacteria causing attaching and effacing lesions
EPEC
EHEC
Requirements for attaching/effacing lesions
1) Tir
2) Intimin
Tir 1) 2) 3) 4)
1) Translocated intimin receptor
2) Secreted by bacteria, inserted into host cell membrane
3) Extracellular component binds intimin
4) Intracellular N- and C- termini bind host cytoskeleton
Intimin
1)
2)
1) 94kDa outer membrane protein
2) Afimbrial adhesin
Function of Tir intracellular regions
Disrupt normal actin trafficking
Cause accumulation of actin below tir, forms a pedestal for bacterium
Tir recruitment of actin is dependent on:
1)
2)
3)
1) Nck
2) N-WASP
3) Arp2/3
Relationship between Arp2/3, N-WASP and Nck
Nck joins Arp2/3 and N-WASP to actin
Is EHEC virulent without tir and intimin?
No
Tir structure
Hairpin loop-like structure
Structure of type 3 secretion system
Multiprotein apparatus
Proteins span both cell membranes
Filmentous structure outside of cell
Which bacteria are T3SS found in?
Only in G-
EPEC T3SS components
1) ESPA - Filamentous structure
2) ESPB/D - Insert into host cell membrane
What is the function of ESPA?
Filamentous structure of T3SS in EPEC
What are ESPB/D?
Parts of EPEC T3SS that insert into host cell membrane
What is actin treadmilling?
Polymerisation and depolymerisation of actin
What nucleates actin?
Arp2/3 complex
EPEC binding 1) 2) 3) 4) 5)
1) EPEC attaches loosely to host cell with bundle forming pilus (bfp)
2) T3SS inserts tir, intimin is expressed
3) EPEC binds to host cell with high affinity
4) Tir is phosphorylated by host cell kinase
5) Nck is activated. Recruits N-WASP and arp2/3 to polymerise actin
