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What is C. diff's method of action?
-both toxins glucosylate
(+ glucose) a threonine residue on G proteins
(which control many cell processes) .
-control polymerization / depolymerization of actin -pseudopodia etc -- requires constant turnover.
- -G protein cycle btwn 2 states.
- (bind GDP and GTP mediates effects of protein)
Why are G proteins important?
- control cell processes
- control polymerization/depolymerization of actin -pseudopodia etc - requires constant turnover.
- cycles btwn GDP and GTP
Where does the A and B toxin act on the GDP-bound form ?
the threonine residue (that's exposed to be glucosylated)
-in GTP form the threonine is buried in protein and inaccessible to toxin
What is the result of action of A and B toxin?
reduces GTPase activity of protein and increases release of GTP from GTP-bond form (glucosylated-GTP bound form has a lower affinity for GTP)
Control of toxin gene expression
- tcdA /tcdB toxin genes are located on PaLoc pathogenicity island present in all toxogenic strains.
- Under the control of regulatory genes tcdC (down) and tcdR (up)
- Toxin levels highest in late-exponential phase of growth
- Transcription and expression of tcdR is highest in early exponential phase leading to expression of A and B toxins• When toxins build up to highest level, tcdC is expressed which counters tcdR decreasing the expression of the toxin
- tremendous energy expenditure - 5% of total protein (in-vitro pure cultures) - very powerful toxins and small amounts can cause severe reactions.
- What do the bacteria get in return for this
- Why should there be this control – more toxin the better ???
- - Nutrients
How do you treat C. diff?
-replace antibiotic causing problem w/ vancomycin or metronidazole (kills c.diff but doesn't affect norman flora)
How do you prevent C. diff?
at early diagnosis (antibiotic associated diarrhea), monitor for A & B toxins in feces.
What's an alternative therapy for C.diff?
-replace resident flora using enema containing dilute feces 4rm fam. member.
(use fecal bacteriotherapy/ fecal micriobiota transplantation (FMT))
What is an enema?
procedure of introducing liquids into rectum and colon via anus
What are the historical potential reasons for increased CDAD ?
- changes in underlying host susceptibility
- changes in antimicrobial prescribing
What are the recent potential reasons for increased CDAD?
- new strain w/ increased virulence
- (CDT-binary toxin)
- variations in TcdB activity
- changes in infection control practices
What is PulseNet?
detection of Foodborne Disease by Pulsed-Field Electrophoresis (PFGE)
What organisms are made up of spirochetes?
Treponema pallium & syphilis
What are the characterisitics of spirochetes?
- Gram (-)
- Thin helical
- Motile, corkscrew style of movement
- Internal flagella
What are organisms that are spirochetes?
- Borrelia burgdorferi - Lyme Disease
- Treponema pallidum - Syphilis
What is the morphology of spirochetes?
Peptidoglycan btwn 2 membranes
What is the physiology and motility of spirochetes?
- has a protoplasmic cylinder
- 1 to many internal flagella emerge 4rm poles (endoflagella)
- covered by multilayered, flexible membrane (outer sheath)
How does the motility work for spirochetes?
- endoflagella rotate -protoplasmic cylinder is rigid and outer sheath is flexible. When flagella rotate in same direction, the protoplasmic cylinder rotates in opposite direction.
- this tension placed on cell causes flexing, twisting, jerky corkscrew movement.
- effective in viscous solution, blood and tissues.
What disease has similar progression to Lyme Disease?
-Syphilis; both caused by spirochetes (but diff genera)
What do Lyme Disease and Syphilis have in common?
multiple stages in their life cycles