Topic 1-14 (Lecture 14)

Question 1

How are Escherichia coli sub-species classified by?

Answer 1

Strain designations

Question 2

What are general characteristics of E. coli?

Answer 2

Gram negative

Multiple strains and serotypes

Question 3

What does EHEC stand for?

Answer 3

Enterohemorragic Escherichia coli

Question 4

What disease does EHEC infection cause?

Answer 4

Severe enteritis (gastrointestinal disease), possibly Hemolytic uremic syndrome (HUS; characterized by damage to kidneys)

Question 5

What are the symptoms of EHEC infection?

Answer 5

Severe nausea, vomiting, cramps, diarrhea, fever, bloody diarrhea

Question 6

What is the usual course of EHEC infection?

Answer 6

Self-limiting; however potentially deadly in immunodefecient/immunocompromised hosts (ex. children, elderly, immunocompromised hosts such as AIDS patients)

Question 7

What is the name of a particularly infectious EHEC serotype with a low ID50?

Answer 7

0157:H7 EHEC serotype

Question 8

How does E. coli cause disease?

Answer 8

Extracellular toxin called Shiga toxins (STX)

Question 9

What type of toxin is Shiga toxins, and where does it bind to?

Answer 9

It is an extracelluar toxin from the “Shiga” toxin family; it is an AB5 protein and binds to host cell receptor Gb3 (found in many types of cells)

Question 10

Where are Gb3 receptors found?

Answer 10

Many cells in body; particularly of note; endothelial cells of blood and lymph vessels (allows toxin to spread into other cells via bloodstream) and human kidney cells (explanation for HUS disease development)

Question 11

How does STX enter cells and cause damage?

Answer 11

1. AB5 toxin enter endothelial cell (usually via endocytosis)
2. STX can trancytose and transit to deeper cells OR travel in retrograde direction through endomembrane system (endosome → Golgi → ER)
3. In ER, A and B subunits seperate, and A is extruded into cell cytoplasm
4. A subunit starts damaging cell

Question 12

What does STX “A” subunits target?

Answer 12

Target host cell protein synthesis machinery, specifically ribosomal 28s rRNA by modifying its structure. Result: Protein synthesis inhibition resulting in cell death and severe inflammation

Question 13

How does EHEC-human transmission occur?

Answer 13

Occurs via fecal-oral route via a number of animal-human contacts (likely result of contaminated fecal material from cattle)

Question 14

Why do cattle not have any symptoms when carrying EHEC?

Answer 14

They do not express Gb3 receptor proteins, thus STX B subunits cannot be endocytosed and cause disease

Question 15

What are some sources of EHEC that could result in human infection?

Answer 15

Ingestion of foodstuffs with from animal shedding; ex. contaminated water, meat products, vegetables, apple drinks, milk (raw)

Question 16

What are some factors that help EHEC survive and colonize the human body?

Answer 16

Has (at least 3) systems to produce compounds to neutralize acid (to survive acidic conditions in digestive tract)

Can create “attaching and effacing” (A/E) lesions on host cells to avoid extrusion via natural fluid flow as well as protection from immune cells

Question 17

How does EHEC produce A/E lesions on host cells (in all host species)?

Answer 17

1) Attaches with specialized pili
2) uses special Type III secretion system to inject the “Tir” (translocated intimin receptor) into the cell
3) Tir become partially imbedded (parts inside and out of cell)
4) Bacterial “intimin” protein binds to Tir
5) Tir gets phsophorylated and takes control of actin cytokeleton, causing the formation of a “pedestal” at EHEC attachment

Question 18

How is EHEC infection treated?

Answer 18

Hydration, as infection is self limiting.
Antibiotics are NOT recommended as they can cause increased express of STX (and thus cause more damage)
Dialysis may be required for those with HUS symptoms

Question 19

What is an example of non-human vaccines to treat EHEC?

Answer 19

EHEC 0157:H7 cow vaccine - vaccinate cows purposefully using avirulent Tir strain. Result was massive decrease in EHEC shedding, indicate the effectiveness of the vaccine

Question 20

Why was the “cow vaccine” for EHEC not implemented?

Answer 20

No incentive from agriculture industry to do so

Government did NOT intervene