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This is a fairly difficult question to answer. Most readings will only tell you that bile salts and crystal violet inhibit gram-positive growth but do not say why. I found some articles that probably would tell us why, but you must pay to subscribe to them. I do know why crystal violet inhibits gram-positive growth though. Crystal violet binds to the peptidoglycan layer of cell membrane in gram-positive bacteria (just like it does in the Gram stain). Gram-negative bacteria have an outer membrane that prevents the crystal violet from attaching to their peptidoglycan layer. Once crystal violet attaches to the peptidoglycan, enzymes called autolysins are unable to cut the polysaccharide linkages between the NAG and NAM residues. The cutting and reforming of the peptidoglycan layer is necessary for cell growth, thus killing the cell. I believe that bile salts work a very similar way just like how penicillin and lysozymes do.

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14y ago
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9y ago

Selective contains bile salts and crystal violet that inhibit the grow of Gram plus organisms selects for gram organisms. Differential- contains lactose and pH indicator (neutral red)- differentiates between lactose fermenters (reddish colonies) and non-fermenters (clear to colorless colonies).

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13y ago

Most gram-positive bacterial cells have a very thick, rigid peptidoglycan cell wall. The abundance and thickenss (25mm) of this material may be one reason why they retain the crystal violet in the Gram stain.

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13y ago

Most gram-positive bacterial cells have a very thick, rigid peptigdoglycan cell wall. The abundance and thickenss (25mm) of this material may be one reason why they retain the crystal violet in the Gram stain.

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11y ago

The mode of action put forward by Steam & Stearn (1928) that the action of crystal violet is due to the formation of an unionized complex of bacteria with dye, is supported. Gram-negative organisms, such as E. coli, have high isoelectric points and contain less acidic components than Gram-positive bacteria which usually have lower isoelectric points, so the former combine with crystal violet less readily and are more resistant to the dye. In extension of this theory, the negative charge on bacteria is increased as the pH of the medium is increased, and the organisms become more sensitive to dye.

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11y ago

because it cannot be trapped by peptidoglycan layer

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12y ago

Ask Kenneth yu

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Q: Why do Gram positive bacteria retain crystal violet stain and remain purpule?
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Related questions

What is the function of safranin in the Gram staining process?

Crystal violet is used first to stain all bacteria purple. However, when you immerse the bacteria then in alcohol, alcohol affects the permeability of the peptidoglycan layer to crystal violet, blocking its exit from gram-positive cells. This way, gram-positive cells remain purple while gram-negative cells are colourless. Safranin red is then used as a counterstain to make the two types of bacteria more differentiable.


What happens if not enough alcohol is applied to a gram stain?

Both bacteria types would be stained by the safranin. When the iodine is added, safranin would be "set" in the positive. The decolorizer would wash out the safranin and then application of the crystal violet would stain the negative.


What is the stainning method called that can distinguish between two different types of eurobacteria?

I believe what you're looking for is the stain that can differentiate between Gram-negative and Gram-positive bacteria: two types of eubacteria. So the staining method is called the Gram method. Crystal violet will remain trapped in Gram-positive bacteria due to their thicker cell walls, causing them to stain purple. Crystal violet can be washed out of Gram-negative cell walls after alcohol treatment to remove their outer lipid membrane, and the cells can be counterstained with a red, positively charged stain. In the end, Gram-positive bacteria will look purple, and Gram-negative bacteria will look red. See Wikipedia for more details.


Function of Gram's iodine?

Iodine is used as a mordant in the gram staining procedure to make large crystals when it is used with crystal violet dye. In gram positive cell walls those crystals get stuck and wont get washed off with the alcohol. In gram negative cell walls the crystals are washed out.


What is the function of iodine solution in the gram stain?

It allows the primary stain crystal violet to remain in the cell instead of being washed out. Due to the larger size of the crystal violet molecule, when the ethanol is applied (the decolorizer) the stain will not be washed out of the Gram (+) positive cells.


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