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Which dye stains gram-negative bacteria pink during the Gram stain procedure?
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9. Microscopes
Gram Stain
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Which of the following correctly lists the sequence of reagents used in the Gram stain procedure?
A
Alcohol, safranin, crystal violet, iodine
B
Safranin, alcohol, iodine, crystal violet
C
Iodine, crystal violet, safranin, alcohol
D
Crystal violet, iodine, alcohol, safranin
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Understand that the Gram stain procedure is a differential staining technique used to classify bacteria into Gram-positive and Gram-negative based on their cell wall properties.
Recall the sequence of reagents used in the Gram stain: first, the primary stain (crystal violet) is applied to stain all cells.
Next, the mordant (iodine) is added, which forms a complex with crystal violet, helping it to fix inside the cell wall.
Then, the decolorizer (alcohol or acetone-alcohol) is used to wash out the stain from Gram-negative cells but not from Gram-positive cells due to their thicker peptidoglycan layer.
Finally, the counterstain (safranin) is applied to stain the decolorized Gram-negative cells pink/red, while Gram-positive cells remain purple.
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