Multiple Choice
Which of the following statements best describes the effect of autoclaving on bacterial endospores?
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11. Controlling Microbial Growth
Introduction to Controlling Microbial Growth
Multiple Choice
During the Gram staining procedure, for how long should the bacterial smear be washed with alcohol (decolorizer) to ensure proper differentiation between Gram-positive and Gram-negative bacteria?
A
Less than 1 second
B
5-10 minutes
C
1-2 minutes
D
10-20 seconds
Verified step by step guidance1
Understand the purpose of the decolorization step in Gram staining: it differentiates Gram-positive bacteria (which retain the crystal violet stain) from Gram-negative bacteria (which lose the stain and take up the counterstain).
Recognize that the decolorizer (usually alcohol or acetone-alcohol) must be applied for a precise amount of time to avoid over- or under-decolorization, which can lead to incorrect results.
Recall that the typical recommended time for washing the bacterial smear with alcohol is short, generally around 10-20 seconds, to effectively remove the crystal violet from Gram-negative cells without affecting Gram-positive cells.
Note that washing for less than 1 second is usually insufficient to remove the stain from Gram-negative bacteria, while washing for 1-2 minutes or 5-10 minutes is excessively long and will over-decolorize, potentially removing stain from Gram-positive bacteria as well.
Therefore, the correct approach is to apply the alcohol decolorizer for approximately 10-20 seconds, carefully monitoring the process to ensure proper differentiation.
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