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87 Cards in this Set
- Front
- Back
Describe regular, commensal E. coli strains.
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Abundant part of microflora in the intestine
Rarely cause disease Some strains are used as probiotics |
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What kind of diseases do pathogenic E. coli cause?
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Diarrhea
Dysentery Hemolytic uremic syndrome (kidney) Urinary tract infections Septicemia Pneumonia Meningitis IBD (inflammatory bowel disease) |
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How do you keep tract of/differentiate between different strains?
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Serotyping reactivity of surface antigens to antibodies
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What is a serogp?
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O: O-Ag of LPS
160 serogps, most are normal flora |
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What is a serotype?
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H: hauch=flagellum
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Describe regular, commensal E. coli strains.
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Abundant part of microflora in the intestine
Rarely cause disease Some strains are used as probiotics |
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What kind of diseases do pathogenic E. coli cause?
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Diarrhea
Dysentery Hemolytic uremic syndrome (kidney) Urinary tract infections Septicemia Pneumonia Meningitis IBD (inflammatory bowel disease) |
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How do you keep tract of/differentiate between different strains?
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Serotyping reactivity of surface antigens to antibodies
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What is a serogp?
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O: O-Ag of LPS
160 serogps, most are normal flora |
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What is a serotype?
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H: hauch=flagellum
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What is K?
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Capsular antigen
(K1 is the leading G- organism that cuases neonatal meningitis) |
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What is virotyping based on?
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Virulence factors
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How is virotyping determined?
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DNA hybridization or PR virulence factor genes
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What are some virulence ass't characteristics?
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Attachment to host cells
Effects of attachment Toxins Invasiveness |
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What are common virotypes of E. coli?
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ETEC: enterotoxigenic
EAggEC/EAEC= enteroaggregative EPEC: enteropathogenic EHEC:enteroheorrhagic DAEC: diffusely adhering EIEC: enteroinvasive UPEC: uropathogenic AIEC: adherent/invasive |
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How many serogps/types does 1 virotype usually have?
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More than 1
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What is the most common EHEC strain?
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O157:H7
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How are E.coli clasified by adherence?
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Localized adherence: ETEC, EHEC, EPEC
Stacked brick: EAEC |
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How are E. colis classified in an outbreak situation?
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Isolate organism from samples of infeted patients
Antibiotic resistance profile serological evidence Genotyping |
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How do E. coli strains become pathogenic?
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Acquisition of virulence factors
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What defines a virulence factor?
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Confers increased ability to colonize/survive/persist/cuase disease in the host
Includes toxins, adhesins, secreted factors, iron acquisition systems |
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What are Falkows postulates about virulence factors?
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1) Gene encoding factor present in strains of bacteria that cause the disease
2) Not present in avirulent strains 3) Disrupting the gene reduces virulence 4) Re-introduction of gene restores virulence 5) The gene is expressed during infection 6) Specific immune response to gene protects (not necessarily) |
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How does E. coli acquire virulence factors?
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1) Gain of genes from mobile genetic elements
2) Black holes: loss of genes that cause increased virulence (not that common) |
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What are the mobile elements that cause gain of genes? For which strain of E. coli?
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Plasmids: ETEC toxin genes
Transposons: ETEC heat-stable toxin (ST) Pathogenicity islands: EPEC, EHEC Bacteriophages: EHEC shiga toxin (Stx) |
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What is the difference btw a pathogenic EHEC strain and K12?
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EHEC has extra 1.3 Mb
->Pathogenic strain has extra DNA compared with the non-pathogenic strains |
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Do all E.coli strains have the smae mode of pathogenesis?
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No
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What does ETEC do?
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Cause watery diarrhea in ppl who aren't previously exposed
-One of the most common bacterial cause of diarrhea in kids in the developing world -Traveller's diarrhea -Can cuase death in children |
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How many ETEC bacteria are needed to cause disease in a healthy person?
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10^8 - 10^10
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What is required to recover from this infection?
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Generally just wait it out and drink water
Don't need hospital or antbiotics |
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How does ETEC cause infection?
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Adheres to intestinal mucosa
Does NOT invade cells Produces toxins that act on mucosal cells, causing diarrhea |
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What is required for ETEC adherence?
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Colonization factor Ags (CFAs)
-Fimbriae mainly found in ETEC strains More than 20types CFA/I/II/III/IV ass't with ETEC strains that cause human disease |
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What are the ETEC enterotoxins?
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LT: heat labile toxin
ST: heat-stabile toxin ETEC strains can have one or both of these |
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How are these enterotoxins encoded?
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In plasmids
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Describe ETEC's LT.
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AB toxin
Closely related to cholera toxin has 1 A subunit and 5 B subunits |
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Describe the mechanism of action of LT-1.
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B component binds a receptor on the host (GM1 ganglioside surface receptor)
A subunits is engulfed A (catalytic domain) ADP-ribosylates stimulatory G ptns (Gs) -Gs regulates adenylate cyclase ADP-ribosylation of Gs constitutively activated a.c. -inc cAMP and cAMP dependent kinases -Activates CFTR (main Cl- channel of epithelial cells) **-Inc Cl- secretion** -Ion imbalance: loss of control over water= diarrhea |
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What are the 2 heat stable toxins?
In what do they cause disease? |
STa and STb
STa: human disease STb: animal disease |
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Describe STa (aa-wise, how many as a precursor etc)
What is its receptor? |
72 aa precursor in periplasm
54 aa peptide to extracellular fluid 17 aa mature form Receptor: guanylate cyclase Causes increase in cGMP, activates kinases, get fluid loss |
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What is the end result of ETEC toxins?
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Secretion of water into the intetinal lumen
Inhibition of NaCl absorption => Watery diarrhea |
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What therapy can be used for ETEC?
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Oral rehydration
->Illness is self-limiting |
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What does EAggEC/EAEC cause?
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Persistent diarrhea in children and AIDS patients
Causes traveller's diarrhea Resembles ETEC in clinical presentation and response to antibiotics |
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Where does EaggEC bind?
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Small intestine
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What form does it take when it binds?
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Stacked brick appearance
->clumps when it binds small intestine |
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What is the adhesin of EAggEC?
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Aggregative Adherence Fimbriae (this is in many, but not all EAEC strains)
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Is EAggEC an invasive species?
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No
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What kind of toxins does EAggEC have?
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No single virulence factor has been irrefutably ass't with EAggEC virulence
-> very heterogeneous gp Some toxins: ST-like toxin, ShET, hemolysin etc |
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What other group is EIEC (enteroinvasive) closely linked to?
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Shigella
(would be the same gp if classified today) |
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What disease do both Shigella and EIEC cause?
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Dysentery: abdominal cramps, diarrhea, vomiting, fever, chilld and generalized malaise
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How many organisms are required to cause infection?
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<10
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Describe the pathogenesis of EIEC
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Invasion
Escape from vacuole Actine based cytoplasmic movement Cell-cell spreading |
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Do EIEC species produce toxins?
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No, whole bact gets engulfed into the cell
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What kind of secretion system does EIEC use?
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T3SS
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Describe the T3SS of EIEC
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Encoded by ~20 genes
Present in many G- pathogens Absent from non-pathogenic bacteria Secretion triggered by contact with host cells ->though the genes used to create the secretion system are similar between different species, the ptns secreted vary a lot |
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What do T3SS look like?
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Molecular syringe
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What is pWR100?
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Virulence plasmid
Found in EIEC and Shigella |
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What does pWR100 encode?
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T3SS
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What happens if there is no T3SS?
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Can't invade host cekk
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What do the effector ptns secreted by the T3SS cause?
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Actin cytoskeleton rearrangements
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What does the cytoskeleton consist of?
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Actin microfilaments
Microtubules Intermediate filaments |
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What is the actin cytoskeleton important for?
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Cell shape
Microvilli Cell migration Cell/cell interactions Cell/ECM interactions Phagocytosis Cell division (cytokinesis etc .: good target for many pathogens |
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How does actin exist? (what form)
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Monomer (G-actin)
Polymerized into filaments (F-actin) |
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How are filaments organized?
Where are monomers added? |
Filaments are directional, have a + and - end
Monomers added at the + end ->Highly regulated process |
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What complex stimulates actin polymerization?
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Arp2/3
Formins can also nucleate actin polymerization |
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What activates Arp2/3?
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WASP family ptns
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Which host family ptn regulates this process?
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Rho family
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What does the Rho family do?
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Acts as a switch btw GTP and GDP
When Rho is attached to GTP, it is active and causes a downstream response, usually linked to the actin-cytoskeleton When Rho is linked to GDP, it is inactive |
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What happens when activated Ras is injected into a cell?
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Lamellipodia (2D sheet-like projections)
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What happens when activated Rho is injected into a cell?
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Stress fibers = contractile bundles of actin and mysoin II
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What happens when activated Cdc42 is injected into a cell?
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Filopodia= 1D projections
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What is actin used for by the bacteria?
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Uptake and cytoplasmic movement within the host
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Describe Shigella invasion (similar to salmonella invasion)
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Use many T3SS effectors
IpgB1, VirA: activate Rac IpgB2: activates Rho IpgD: causes disconnection of actin from PM =>These regulate actin cytoskeleton => Cause mb ruffles around bacterial point of entry |
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What happens if IpgB1/IpgB2 is KO?
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Decrease invasion
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How does Shigella escape from the vacuole?
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T3SS, but mechanism is unknown
Mb fragments releast from the vacuole act as DAMPs and trigger host cell signalling responses including cytokine producton, autophagy and pyroptosis |
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How do EIEC/Shigella spread from cell to cell?
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Hijack host cell's actin cytoskeleton and use it to spread within and between cells
pWR100 plasmid encoded IcsA binds and activates N-WASP (which activates Arp2/3 which activates actin) IcsA is expressed at one pole of the bacterial cell Actin polymerization behind the bacteria gives it a propulsive force |
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What happens if you KO IcsA?
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IcsA is what Shigella binds, in order to activate actin polymerization
Won't be able to leave cell |
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What kind of disease is EPEC (enteropathogenic) responsible for?
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Neonatal diarrhea in developing world
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What are the 3 stages of EPEC host cell interaction?
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1) non-intimate binding (bundle forming pili) Bfp
2) Type III secretion 3) Intimate binding (pedastal formation*) |
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Does EPEc enter the host?
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No, stays extracellular
->Uses its T3SS to inject effectors into the host ->Reprograms cell biology |
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What does EPEC secrete into the host through its T3SS?
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TIR (translocated interim receptor)
Once in host, TIR integrates itself into the host cell mb and serves as a receptor for effector ptns ->EPEC has its own receptor for tight injection, .: it can infect many different types of cells |
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What are teh main players in EPEC pedastal formation?
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Locus for Enterocyte Effacement (LEE) pathogenicity island
This PI encodes: -a T3SS -T3SS effector ptn Tir -Outer mb ptn Intimin |
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What are the steps to pedastal formation?
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1) EPEC Tir is inserted into the host cell plasma mb in a hairpin configuration
2)Extracellular loop binds intimin on bacteria 3) Intracellular tyrosine is P and initiates actin polymerization 4) P of Tir: allows binding of NCK (adaptor): which binds many things, including P Tir and N-WASP |
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What happens to the host cell once the T3SS is in place?
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Microvilli disappear
Form a pore in the host using T3SS (this pore is a conduit btw the host cell cytoplasm and bacterial cytoplasm) Tir goes into host Bacteria bind internin on the surface Tir important for clustering on cell Get directional polymerization of actin due to NCK ->Cause pedastal formation |
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Why does this bacteria form a pedastal?
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Strong, tight interaction with host
->Will be flushing of the system soon, so if bacteria tightly bound, won't get flushed out of host |
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What is EspF important for?
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Tight junction disruption during EPEC infection
(EspF is a T3SS effector ptn) |
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Why is it important to disrupt the tight junctions?
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Can invade between cells, instead of through them
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What is occludin?
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Tight jct ptn
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What happens to occludin during infection with WT EHEC?
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Lose them
Get disruption Bacteria can get to the tissue |
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How does EPEC cause disease once it attaches to the host?
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Unclear
Effacement of microvilli: loss of absorptive surface Destruction of tight jcts btw intestinal epithelial cvells Signal transduction in host cells Leading to alterations in wate and electrolyte absorption and secretion (change amount of ions that can go into and come out of the cells) |