Multiple Choice
Why is it important to use fresh bacterial cells when performing a Gram stain?
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9. Microscopes
Gram Stain
Multiple Choice
Which of the following describes the correct sequence of the Gram stain procedure?
A
Crystal violet, iodine, alcohol, safranin
B
Iodine, crystal violet, safranin, alcohol
C
Safranin, alcohol, iodine, crystal violet
D
Alcohol, crystal violet, safranin, iodine
Verified step by step guidance1
Understand that the Gram stain 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 procedure: 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 applied 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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