Enteropathogenic and Enterohaemorrhagic E.coli Flashcards
What age group is EPEC most common and what is the mortality rate?
<2 years with a >30% mortality rate
What are symptoms, Route of infection and reservoirs of infection for EPEC?
- Diarrhoea, Vomiting, Fever
- Route of infection: Faecal-oral transmission, contaminated surfaces, infant food, water, hands
- Reservoirs of infection: Asymptomatic and symptomatic children, asymptomatic adult carriers, mothers and persons handling children
Does EPEC produce toxins? Is it invasive?
No, Non invasive.
How is EPEC defined? (by the presence of…)
Presence of LEE and Bfp
What is the difference between a typical EPEC and an atypical EPEC?
Typical EPEC has bfp atypical does not
How does EPEC attach and efface lesions? (3 stages)
- Stage 1: Non-intimate association via bundle forming pili
○ Bacterial cells aggregate together - Stage 2: Type 3 secretion of Tir and other effectors
○ Assembly of Type III secretion system which
leads to intimate adherence
Stage 3: Intimate adherence, Attaching and Effacing lesion
What is a Bundle forming pili? How is It regulated? What is it’s importance in virulence (EPEC)
- Mediates bacterial-bacterial interaction -> forming of microcolonies
- Transcription of bfp regulated by Per A
- Encoded by PerABC operon on EAF plasmid
- Per B and C required for full transcriptional activation of the bfp gene cluster
- Importance in virulence: mediated initial adherence to host through n-acetyl-lactosamine receptors on host cell
What is a pathogenicity island?
- A segment of a plasmid with genes encoding for virulence factors
- Usually large but unstable due to ‘mobility’ genes
What does LEE stand for and do? How many operons are there? Why is it necessary? (EPEC)
- Locus of Enterocyte Effacement (LEE)
- 5 operons, in order - 1,2,3,5,4
- Necessary for the attaching and effacting effect and pedestal formation
What does each Lee operon encode? (EPEC)
- LEE1-3
○ Encodes type 3 secretion system (TTSS) for
translocating bacterial proteins towards the
enterocyte - LEE4
○ Encodes esp genes (EPEC secretion proteins)
espADB encode for translocator proteins that form
a conduit through which T3SS delivers effector
proteins to host cell - LEE5
○ Encodes genes necessary for bacterium-host cell
intimate adhesion (eae: encodes adhesin intimin,
tir: Translocated intimin receptor)
How do EPEC secrete effector proteins into host cells using the T3S system?
- Inner and outer ring components assembled
- EscF polymerized and assembled into outer and inner rings
- EspA filament secreted via type 3 secretion system and attached to the tip of the needle
- Formation of a hollow filament
- Translocation effector proteins enter into host cell
What is the role of T3SS in intimate adherence? (EPEC)
- Intimin used to cause intimate binding, however there is no natural receptor for it
- Tir (translocated intimin receptor) is translocated into host cell via T3SS and acts as a receptor for intimin
How does Tir activate an actin signaling cascade? (EPEC)
- Tir becomes tyrosine phosphorylated in host cell plasma membrane
- Binds to adaptor protein
○ Nck - Nck recruits N-WASP or a WIP-N-WASP complex
○ Triggers activation of the Arp2/3 complex - Actin is assembled in a pedestal formation
How does EPEC cause diarrhea?
- Damage to absorptive apical surface causes failure to absorb water
- Injected effector proteins disrupt tight junctions
○ Increases permeability of mucosal enterocyte tight
junctions
○ Activation of NFkb
○ Activation of IL-8 cytokine - Recruitment of polymorphonuclear neutrophils (PMNs)
What diseases can EHEC cause?
- Diarrhoea
- Bloody stools
What is the origins of an EHEC?
- Originally an atypical EPEC which acquired a shiga-like toxin via a bacteriophage
Explain the pathogenesis of EHEC
- Similar to EPEC
- LEE pathogenicity island present
- Forms A&E lesions
- Produces large amounts of shiga-like toxin which acts on sites remote from intestine
Explain EHEC and adhesion?
- No bfp
○ Uses wide variety of adhesions - Mediate similar binding and actin rearrangements as EPEC
- Use Intimin (eae) adhesion to intimately attach to host cells
Explain actin signalling cascade activated by EHEC during pedestal formation
- Tir localizes to the plasma membrane
○ NOT tyrosine phosphorylated - Tir binds IRTKS/IRSp53
- The EHEC effector EspFu links complex to N-WASP
- N-WASP stimulates Arp2/3 nucleation of actin
Pedestal formation
What toxin does EHEC produce? What are the 2 immunologically distinct types and how do they differ?
- Shiga-like toxins
- Stx1, st2
○ Stx2 is associated with severe human disease
How are Shiga-like toxins encoded? (EHEC)
Encoded within lysogenic bacteriophage
Explain the structure of Shiga-like toxins (EHEC)
Ab5 type toxin, active part central with b part surrounding
What is the receptors for Shiga-like toxins (EHEC)
Gb3
Explain the mechanism of action of Stx toxin (EHEC)
- In kidney B subunit of toxin binds to Gb3 which is expressed on cell surface
- Shiga-like toxin damages blood vessels and kidney cells
- Action of damage is:
○ External toxin enters clathrin coated pit
○ Coated vesicle is formed
○ Fusion of lysosome with coated vesicle
○ Toxin is processed in cytosol
○ A1 cleaves 70S ribosomes which inhibits protein
synthesis
