E. Coli Flashcards by Steph Morton

Differentiate between commensal E. coli and enteropathogenic E. coli.

Commensal E. coli: part of normal intestinal microflora (0.1%)

-Make vitamin K and some B vitamins
-Protects against other pathogens at mucosa

E. coli intestinal pathogens are STRAINS that have acquired VIRULENCE FACTORS through horizontal gene transfer

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Understand the processes involved in the “evolution” of a pathogen.

Evolve by HORIZONTAL GENE TRANSFER via..

-Phage
-Plasmids
-Transposons
-Gene loss

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List the toxins secreted by each of the six E. coli strains discussed.

EHEC: STX, hemolysins
ETEC: ST, LT
EPEC: no toxins
EAEC: hemolysins, EAST
EIEC: no toxins
DAEC: no toxins

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List the shiga toxin-producing E. coli (1) and the diarrheagenic E. coli. (4)

Shiga toxin-producing EC (STEC):
EnteroHemorrhagic EC (EHEC)

Diarrheagenic: (PATI-D)
EnteroPathogenic EC (EPEC)
EnteroAggregative EC (EAEC)
EnteroToxigenic EC (ETEC)
EnteroInvasive EC (EIEC)
Diffuse Adhering EC (DAEC)

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What is the most common EHEC serogroup?

O157:H7

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How is EHEC spread? What is its infectious dose?

Foods:
--Undercooked/contaminated ground beef
--Leafy vegetables
--Unpasteurized apple cider/juice
--Raw-milk dairy products
Animals (house pets, petting zoos)
Person-to-person contact

Infectious dose: very low, 100

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What are the clinical symptoms of EHEC?

Abdominal pain
Bloody diarrhea
**Hemolytic uremic syndrome - can -> renal failure

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What are the symptoms of hemolytic uremic syndrome? (4) What causes it? How can it be treated?

Destruction of RBCs, damage to lining of vessel walls due to apoptosis/necrosis; hemolytic anemia; thrombocytopenia

Caused by shiga-like toxin (STX) from E. coli

NO antibiotics (increase toxin production)
Treat with fluid management to protect kidney

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Briefly list the steps of EHEC pathogenicity.

EHEC cells remain extracellular in gut (no bacteremia) - TOXIN gets into bloodstream

Attachment via common pillus -> effacement
T3SS mediated change in host cells by injection of Tir -> Tir-Intimin binding -> tight interaction
Actin polymerization and pedestal formation
Release of HEMOLYSIN, SHIGA-like toxin, and other factors

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Why can animals carry EHEC without getting sick?

Shiga toxin binds a host glycolypid that is different between cattle and humans

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What does EPEC cause? How is it transmitted?

Childhood diarrhea (MANY cases)
Transmitted person to person

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What does ETEC cause? How is it transmitted?

Traveler’s diarrhea, esp. in infants in developing word

Food/water
Person to person

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What E. coli type causes the most epidemics?

STECs

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Describe how EHEC binds to the gut, including virulence determinant involved.

Uses E. coli common pilus (same as commensal E. coli)

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What is the pathogenicity island in EHEC? What does it encode

LEE = Locus of Enterocyte Effacement

-Encodes T3SS and effectors
-Encodes Tir and Intimin

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How does the T3SS in EHEC function?

Induced by many things, including contact with host cell

EspA = needle
EspB/D pass through needle to tip -> form pores in eukaryotic membrane for proteins to pass through

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How is the attachment of the T3SS in EHEC to the host cell promoted? Why? (know this)

Promotes attachment by creating its own receptor:

-Injects TIR into host cell -> exposed on host cell surface
-Expresses INTIMIN on its own membrane
-Tir and Intimin interact with each other, binding tightly

Doesn’t have much time, needs to attach to wall as it is moving along - this helps it attach faster

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What is effacement? What is another name for it? Why does it occur? What results?

Loss of host cell microvilli
AKA A/E lesions
Occurs because host cell reabsorbs microvilli in response to attachment of E. coli

Results in DIARRHEA: reduced microvilli -> reduced absorption

What happens when EHEC is firmly attached to a host cell?

Once attached, -> actin polymerization -> changes in cell bio/structure of host cell -> pedestal formation (essential for virulence)

How did EHEC get its shiga-like toxin?

Bacteriophage-mediation transduction

What are the roles of the A and B subunits of Shiga-Like Toxin? (may not need to know)

B = mediates toxin uptake by receptor binding
A = interferes with protein synthesis by messing with 28S rRNA

List the virulence determinants in EHEC. (8)

Common pilus
Shiga-like toxin
T3SS, Tir/Intimin
Hemolysin
Capsule (K-antigen)
LPS (-> inflammation)
Nutrient acquisition pathways

What is the role of hemolysin in EHEC?

Pore-forming protein that inserts into host cell membranes -> lysis

What is the commensal strain of E. coli?

K12

What pathogenicity islands does EPEC have?

T3SS with Tir/Intimin binding (forms A/E lesions) Bundle-forming pili (BFP) for adherence & formation of microcolonies on surface of cells NO toxins known

How does EPEC cause diarrhea?

Effacement from attachment to/microcolony formation on host cell -> decreased absorption

What virulence factors does ETEC have? (3) How do they work?

Fimbriae: help colonize small intestine ``` Labile toxin (LT): similar to cholera toxin, -> watery, slightly bloody diarrhea --Targets AC -> increased cAMP -> inhibition of CFTR -> increased Cl secretion, blocking of Na uptake -> loss of fluid and electrolytes ``` Stabile toxin (ST): -> stimulation of guanylate cyclase -> increased cGMP (similar outcome to that of LT)

List the adhesins used by each of the six E. coli strains discussed.

``` EHEC: Common pilus, A/E ETEC: Fimbriae EPEC: Bundle-forming pili, A/E EAEC: forms biofilms EIEC: nonfimbrial adhesins DAEC: (not discussed) ```

What disease is caused by EAEC? What virulence factors does it have?

More aggressive childhood diarrhea, but similar to EPEC Hemolysins EnteroAggregative Stable Toxin (EAST) Pet (plasmid-encoded toxin)

What disease does EIEC cause? How is it transmitted? What is different about it?

Watery diarrhea with blood and mucous Transmitted via contaminated food Invasive! Can polymerize actin behind it (like Shigella)

What is the adherence pattern of DAEC?

Diffusely adhering!

Briefly describe the O104:H4 epidemic.

Bloody diarrhea, lots of serious complications (with HUS) Caused by EAEC that had picked up the Shiga-like toxin ---NOT by EHEC! Carried by infected bean sprouts

How is E. coli diagnosed?

Stool samples Enrich in Gm- broth PCR -> virulence factors Toxin analysis

E. coli: lactose test

Positive

E. coli: Sorbitol MacConkey Agar

O157:H7 sorbitol negative (red) | Commensal E. coli sorbitol positive (black)

How is EHEC diagnosed?

Sorbitol-MacConkey agar (red) Immunoassay for Shiga toxin PCR for virulence genes

How is ETEC diagnosed?

PCR for virulence genes

How is EPEC diagnosed?

PCR for virulence genes | Tissue culture assay for localized adherence

How is EAEC diagnosed?

PCR for virulence genes | Tissue culture assay for aggregative adherence

How is EIEC diagnosed?

PCR for virulence genes

How is DAEC diagnosed?

Tissue culture assay for diffuse adherence

How is ETEC treated?

For travelers: Loperamide (may use with fluoroquinolones) Azithromycin Rifaximin

How is EPEC treated?

Abx guided by susceptibility testing for sever/protracted cases

How is EAEC treated?

Fluoroquinolones for travelers, HIV patients