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Gram's stain


newbie
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I don't even know where to begin to explain how I started reading up on this, but everywhere I have looked I am getting the same anwsers. Could someone explain in laymen terms what Gram's stain is or does?

http://www.infoplease.com/ce6/sci/A0821504.html

http://www.encyclopedia.com/html/G/Gramssta.asp

 

There are more links but it's all pretty repetitive. What would be the circumstance of having a Gram test done? What does it tell us if it is Gram-positive bacteria or Gram-negative bacteria? Is this something that is routinely done?

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"What would be the circumstance of having a Gram test done?"

 

If you wanted to indentify an unknown bacteria you had cultured, eg. from an infection from someones wound.

 

"What does it tell us if it is Gram-positive bacteria or Gram-negative bacteria?"

 

It tells you which of two basic types of cell wall the bacteria has, which narrows down the possible bacteria it could be.

 

"Is this something that is routinely done?"

 

Yes, it's usually the first stage in identifying a bacteria culture.

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Skye said in post #2 :

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Thanks for the info but what I meant to say was when you identify which cell wall the bacteria has what does that tell us? Can we then identity harmful bacteria? Is this test performed on all bacteria?

 

ps. Sorry for all the questions

 

pps. Have any links with more info would be helpful too. All I can find is the definition.

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newbie said in post #4 :

 

Thanks for the info but what I meant to say was when you identify which cell wall the bacteria has what does that tell us? Can we then identity harmful bacteria? Is this test performed on all bacteria?

 

Ps. Sorry for all the questions

 

Gram positive (meaning they test positive during the gram stain) bacteria have peptidoglycan in their cell wall. It does not tell us which bacteria specifically, but like someone above said, it can be used to rule out certain bacteria (if you know they are gram + or gram -)

 

I think gram negative tend to be more pathogenic..

 

Treatment for the bacteria depends on whether or not it is gram positive or negative.

 

The test is routinly performed in the medical field, almost all cultures have a gram stain test.

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The gram negative bacteria are often pathogenic because they part of their charcteristic cell wall, made of molecules called lipopolysaccharides, is often toxic to animals. Particular molecules that are toxic are called endotoxins.

 

There are plenty of pathogenic gram positive bacteria though.

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I think what blike meant to say was that the gram - bacteria have lipopolysaccharides in their outer membrane. This is what distinguishes the two types. Both the - and the + bacteria have peptidoglycan. This is actually why gram - bacteria do not take up the gram stain, the lipopolysaccharide covers the cell membrane and excludes the stain.

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You are correct, I did mean peptidoglycan though. Gram positive bacteria have about 5 times more peptidoglycan than gram negative bacteria. It is the peptidoglycan that retains the purple dye. Gram negative bacteria, however, do have lipids in their outermembrane.

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  • 1 year later...

The grams stain is one of the most important stains in bacteriology/micro, etc. it pretty much divides bacteria into the 2 groups.

 

Gram positive is the purple/blueish dye, they retain the primary basic dye.

Gram negative happens when the species lose the primary dye and stain a pink/red.

 

The reaction of the bacteria- or colour to the gram stain is pretty much a reflection of the different chemical makeup of the cells of the two groups.

 

Gram positive obviously have a cell wall that contains fats/lipids talked about earlier.. (peptidoglycan)

Gram negative bacteria contains a layer of lipopolysaccharide which is absent in gram positive bacteria.

 

There are heaps of other ways to categorise bacteria.. This does not really group them into the pathogens/non-pathogens, it merely categorises the eubacteria into smaller groups.

 

-morphology/structural characteristics, growth, nutrition, biochemistry serology, genetics, ahh too many to type down- Are a few ways in which you can identify bacteria. The gram Staining is just one! (Of the broadest)

 

In order to find bacteria species and strains, you will have to use categorisation such as biochemistry, phage typing, and protein profiles....

 

*end rant*

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"What does it tell us if it is Gram-positive bacteria or Gram-negative bacteria?"

 

It tells you which of two basic types of cell wall the bacteria has' date=' which narrows down the possible bacteria it could be.

[/quote']

 

 

Excuse me, but I think this is wrong. Gram-negative bacteria have a double cell membrane, while gram-positive bacteria have a single cell membrane. I don't think it has anything to do with a cell wall.

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  • 4 weeks later...

bacteria identification is not revealed through Gram stain, it only divides them into Gram pos or neg bacteria, identification requires a dichotomous key with several biochemical tests designed to match certain characteristic traits of common bacterial species.

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  • 1 month later...

e.coli is right

when we're talking about gram stainning, cell walls should not be mentioned.

(i have learnt this the hard way, thanks to an anal retentive microbio advisor)

to truly understand the mechanisms of gram stainning, we should start using the correct terminology of the structures involved in stainning.

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