jean robert
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34 y.o man is struck by a car and sustains crush injuries to both legs. While hospitalized, he develops a severe infection in the legs and the tissues become hard to the touch and crepitant. A plain x-ray film reveals formation of black pockets in the soft tissues. Which of the following attributes of the most likely causative agent is responsible for the observed muscle pathology?
a) Ability to degrade collagen
b) Ability to degrade DNA
c) Ability to degrade egg-yolk agar
d) Ability to degrade hyaluronic acid
e) Ability to stimulate permeability
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| silver
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confused b/w A or D  
god i need to work on my micro.
i think D
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| pr20
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A.Ability to degrade collagen.
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| new_n_lost
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c) Ability to degrade egg-yolk agar >>>probably gas gangrene Clostridium perferigens ??
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| Tiff
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E? C. tetani
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| angel23
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C.tetani doesnt stimulate permeability....it is the work of lecithinase secreted by C.perfringes....ability to form pores....
so i l go with E
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| latlov
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think d org in question is C.perfringes.it produces lecithinace dt causes myonecrosis,gas gangrene and or hemolysis.its identified by its ability to degrade egg yolk agar(Nagler reaction)
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| Tiff
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ok. c.perfringens makes sense. Especially with the crepitance and hard tissue. Was trying to think of organisms that cause infection in crush injuries - only tetani came to mind. But C. perfingens hence choice c is reasonable. 
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| bactitech
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The organism is C. perfringens. This bug produces LOTS and LOTS of gas quickly in the tissues. I have seen this bug in a positive blood culture before. There is so much gas in the bottle that the rubber septum on the bottle bulges out and if you put a syringe in there to sample the broth for a gram stain, the gas will blow the inside of the syringe out of the main body of the syringe. You need to vent the bottle first before sampling.
In a cooked meat broth, the gas literally raises the pellets of cooked meat off the bottom of the tube. If you inoculate this broth, the bubbles will start within a couple of hours after inoculation. It is fast growing.
Unfortunately this gas production is reproduced in human tissue. This organism was the cause for thousands of limb amputations during the American Civil War.
We used to use an agar called LL Agar - Lactose lecithinase - to identify this. Lecithin comes from eggs. The organism will produce a lecithin precipitate around the colony on a pale purple agar.
However, to answer the question, I would suspect it is C. perfringens' ability to degrade collagen. The gas literally pulls the muscles aparts creating gas pockets inside the tissues. Isn't collagen the substance that binds cells together?
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| jean robert
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new_n_lost wrote:
c) Ability to degrade egg-yolk agar >>>probably gas gangrene Clostridium perferigens ??
The disease described is GAS GANGRENE, which is caused by the spore forming anaerobe C. perfringens and other closely related species. These very dangerous bacteria particularly like to grow in necrotic vascular tissue and they produce a variety of destructive enzymes and toxins.
The toxin produced by C. Perfringens that is most strongly associated with myonecrosis is the alpha toxin, which is a Lecithinase, phospholipase C, that lyses erythrocytes, platelets leukocytes, and endothelial cells.
This toxin mediates massive hemolysis, increased vascular permeability and bleeding,hepatotoxicity, bradycardia,and hypotension. In the laboratory, the action of the lecithinase can be observed in Nagler s reaction, in which strains of C. perfringens will lyse the lecithin in Egg-yolk agar.
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| jean robert
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Ability to degrade collagen is displayed by the Kappa toxin of C perfringens (a collagenase). It contributes to the necrotizing activity of the organism , but is not the most important cause of the myonecrosis.
Ability to stimulate permeability is expressed by the epsilon toxin ( a permease) of C .perfringens. It s produced as a protoxin, is activated by trypsin , and increases the permeability of the GI tract. It s more important as a contributing cause to the development of necrotizing enteritis than to myonecrosis
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| new_n_lost
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jean robert wrote:new_n_lost wrote:
c) Ability to degrade egg-yolk agar >>>probably gas gangrene Clostridium perferigens ??
The disease described is GAS GANGRENE, which is caused by the spore forming anaerobe C. perfringens and other closely related species. These very dangerous bacteria particularly like to grow in necrotic vascular tissue and they produce a variety of destructive enzymes and toxins. The toxin produced by C. Perfringens that is most strongly associated with myonecrosis is the alpha toxin, which is a Lecithinase, phospholipase C, that lyses erythrocytes, platelets leukocytes, and endothelial cells. This toxin mediates massive hemolysis, increased vascular permeability and bleeding,hepatotoxicity, bradycardia,and hypotension. In the laboratory, the action of the lecithinase can be observed in Nagler s reaction, in which strains of C. perfringens will lyse the lecithin in Egg-yolk agar.
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