Toxins

What is a risk assessment?

It is the risk that is tolerable when eating something in the case of a food product

Are toxins secreted from cells? If yes, what is this acting like? Can toxins act alone?

Yes and this is action at a distance. Yes

Describe where bacterial toxins are synthesized

They are synthesized in the cytoplasm of cells and then are secreted across the cytoplasmic membrane and eventually into the extracellular milieu

Can toxins accumulate? When are the effects of toxins worsened?

Yes they can and the effects are worse when bacterial colonization is big (have a ton of bacteria now producing the toxin)

What do toxins tend to exhibit? What is an example of this?

Specific host-cell affinity thereby targeting cell types (or certain organs). An example is E.Coli O157:H7 with binding to Gb receptor on kidney cells.

What contributes to enterohaemorrhagic E.Coli O157:H7 pathology?

Virulence factors

What is the cholera toxin secreted by?

T2SS

What happens if you treat with antibiotics at the wrong time?

Then you get a large amount of the toxin at the same time

What type of toxin is the anthrax toxin?

A-B type with two independent A subunits and a common B subunit

What is the B unit called? What does it bind to? What is PA processed by?

Protective antigen (PA) and binds to TEM8 or CMG2 on host cells. It is processed by a membrane protease (host membrane protease) called furin that then oligomerizes to form a heptameter or octamer (heptamer or octamer of PA)

What does the A subunits bind to?

B subunits on host cells

What are the two independent A subunits? What outcomes do they lead to when they bind to the B subunits?

1. Edema factor (EF)- is an adenylate cyclase. Leads to swelling and fluid accumulation

2. Lethal factor (LF)- is a zinc dependent endoprotease. Leads to cell death as it cuts within proteins

What increases with EF?

cAMP levels

What happens after proteins bind a receptor?

Conformational changes in the protein complex occurs and modifications can also occur

What is an example of a modification that can occur?

Furin cleavage

Describe receptor mediated endocytosis with the anthrax toxin

1. AB engagement induces membrane curvature which in turn promotes endocytic action

2. The AB5 complex is internalized in a early endosome within a hosts cytoplasm

3. The A subunit translocates through the B complex into the cytoplasm

What does endocytic action mean?

An internal action is going to happen

Describe the anthrax pathway

1. Exotoxins such as PA, LF, and EF are secreted from bacillus anthracis

2. PA is going to bind to a receptor on the hosts surface

3. Furin is going to bind to PA and receptor and will cleave PA to activate it

4. PA is going to oligomerize into a heptamer or octamer

5. LF or EF will bind to PA octamer or hetapmer

6. A-B complex will get endocytose and LF or EF factor will be translocated into the cytoplasm of the host

7. EF can combine with calmodulin and ATP to form cAMP that leads to edema

8. LF can cleave MAPKK which leads to cell death

What is EHEC O157:H7 known as? What is the toxin?

Hamburger disease pathogen. Shiga toxin

What is the bacteria for EHEC O157:H7 commonly associated with?

Cow intestine (non-pathology). Cow fecal matter contaminates ground water and has consequences for irrigation, plant, and leafy vegetable crops

What helps colonization of EHEC O157:H7?

Pili, adhesins, T3SS, and effectors

What can the Shiga toxin bind to?

GB3 receptor on host cells and is highly expressed on kidney cells

What does Shiga toxin induce?

Tubular membrane invaginations for its uptake into cells. A conformational change in protein-protein interactions occur at the membrane.

Describe the Shiga toxin pathway

1. Shiga toxin (Stx) binds to Gb₃ receptor on host cell

2. Receptor mediated endocytosis is performed where the Shiga toxin is now in an early endosome

3. Shiga toxin goes through retrograde transport from the golgi to the ER

4. Causes a lot of ER stress as it is not typically there and causes damage which has pathologic effects on the cell

What are three affects Shiga toxin has? Does it have multi-targets?

1. Unfolded proteins in the ER

2. Cleavage of adenine residue in 28S rRNA

3. Induction of cytokines, leukocytes, reactive oxygen metabolites

Yes

What happens if there is unfolded proteins in the ER?

There is an ER stress response that leads to apoptosis

What happens if there is cleavage of adenine residue in 28S rRNA?

You are targeting ribosomal RNA and protein synthesis is no longer going to work. There is ribotoxic stress responses leading to apoptosis of affected cells and ultimately damage to colon, CNS, and kidneys

What happens if there is induction of cytokines, leukocytes, and reactive oxygen metabolites?

TTP, end stage renal disease, hemorrhagic colitis and HUS

What is a hallmark feature of Shiga toxin?

HUS

What are the effects of Shiga toxin?

Systemic effects, kidney failure, and colitis