Pathogenesis Flashcards
Explain the components of exotoxins
They are often 2 subunit A-B exotoxins where the A is for the activity of the toxin. It’s the active subunit; the B subunit is for Binding to the host cell’s receptor so that the toxin can gain entry into the cell
How does the exotoxin for Corynebacterium diptheriae exert its effects?
It inhibits protein synthesis of the host cell by inactivating Elongation factor-2 which eventually leads to cell death
T or F
Exotoxins can only exert their effects on short distances
False
They can act locally as in C. Perfringes which cases gas gangrene or at a distance as with C. tetani that accesses the CNS via transport along axons via the bloodstream
Does V. cholera produce an exotoxin? If so, what is its mechanism of pathogenecity?
It does. It has a A-B subunit exotoxin that when inside host cell will prevent the inhibition of Gs which causes the perpetual stimulation of cAMP which stimulates the opening of the Cl channel. Cl- will continually flow out of the cell taking Na and water with it. This is mass dehydration
What organism is responsible for global paralysis after stepping on a rusty nail?
C. tetanus. It works via ann A-B exotoxin that will prevent the release of inhibitory NTs so that only excitatory NTs are employed. This cause is non-stop stimulation of all muscle in the body. Leads to spastic paralysis, fever, and sweating
What organism is responsible for botulism?
C. botulinum. It can be found in honey. It is anaerobic. It has a A-B exotoxin that when inside a host cell will prevent the release of stimulatory NTs (Ach) so there is flaccid paralysis. This is the opposite of tetani
If you get shady looking mail from someone you don’t know, what should you suspect? Does this bug have an exotoxin you should be worried about?
Suspect Anthrax from bacillus (rod) anthracis. its an aerobe that has 2 toxins made from 3 subunits - 2A and a B.
The B subunit is the “protective antigen” that is used in vaccines and each of the toxins.
One of the A’s is for edema, the other A is for “Lethal Factor”. Scary.
…so Edema-Protective and Lethal Factor-Protective
What is a toxoid?
It is a non-toxic but still antigenic compound that is partially denatured EXOtoxin (either by heat or acid) and is used for immunizations. Exotoxins are highly antigenic and heat labile
What is the difference btwn endotoxins and exotoxins?
Exotoxins are secreted into the extracellular spaces but endotoxins are actually on the bacterial wall. its an integral part of the bacteria. An ex of endotoxin is LPS which is an integral part of gram - bacteria and is liberated when the bacterium lyses and can cause septic shock.
An exotoxin is heat and acid labile, whereas endotoxins are relatively stable. Exotoxins don’t cause fever (except for the pyrogenic toxins), but endotoxins cause fever and septic shock
What kind of toxin is LPS and what part of it is toxic
It is an endotoxin of gram - bacteria.The toxic portion is Lipid A on the outer membrane
How do endotoxins cause septic shock?
When the endotoxin is released into the bloodstream, it is will bind to receptors on macrophages causing cytokine release (IL-1, TNF-a) and activates inflamm response and coag cascades which can lead to septic shock.
Can gram + bacteria cause septic shock even tho they dont have LPS?
Yes they can. It’s prob due to the peptidoglycan wall or the techoic acid which is less toxic than LPS and LPS is less toxic than exotoxin.
Adherence of bacteria to host cell
This is called localization and is the first step of entry, or secretion of proteins into host cell.
Its mediated by adhesin on bacteria and host cell receptors. Abs against adhesins can block this
How does the strain of E. coli that causes pyelonephritis bind to host cells?
This strain of E. coli has to have a P pilus. It has a lot of them and these pili bind to the P blood group antigen. Without this, it can climb its way to the kidney and will just simply cause a UTI
What is the type III secretion sys and what kind of bugs use it?
This sys is used by pathogenic gram - rods to detect euk cells and inject virulent proteins into them. They can infect, survive, and evade host’s immune sys with this sys
They can induce or prevent uptake (Salmonella and Yersinia, resp) and induce or prevent apoptosis (yersinia and chlamidya, resp)
