E. Coli Flashcards
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
Understand the processes involved in the “evolution” of a pathogen.
Evolve by HORIZONTAL GENE TRANSFER via..
- -Phage
- -Plasmids
- -Transposons
- -Gene loss
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
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)
What is the most common EHEC serogroup?
O157:H7
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
What are the clinical symptoms of EHEC?
Abdominal pain
Bloody diarrhea
**Hemolytic uremic syndrome - can -> renal failure
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
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
Why can animals carry EHEC without getting sick?
Shiga toxin binds a host glycolypid that is different between cattle and humans
What does EPEC cause? How is it transmitted?
Childhood diarrhea (MANY cases) Transmitted person to person
What does ETEC cause? How is it transmitted?
Traveler’s diarrhea, esp. in infants in developing word
Food/water
Person to person
What E. coli type causes the most epidemics?
STECs
Describe how EHEC binds to the gut, including virulence determinant involved.
Uses E. coli common pilus (same as commensal E. coli)
What is the pathogenicity island in EHEC? What does it encode
LEE = Locus of Enterocyte Effacement
- -Encodes T3SS and effectors
- -Encodes Tir and Intimin
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
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
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
