Multiple Choice
If a Gram stain result is unclear, which of the following should be considered?
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9. Microscopes
Gram Stain
Multiple Choice
Why is it important to use both positive and negative controls when performing a Gram stain?
A
To verify that the staining procedure is working correctly and to ensure accurate interpretation of results
B
To enhance the growth of Gram-positive bacteria
C
To prevent contamination of the bacterial sample
D
To increase the speed of the staining process
Verified step by step guidance1
Understand the purpose of a Gram stain: it is a differential staining technique used to classify bacteria into Gram-positive or Gram-negative based on their cell wall properties.
Recognize that positive and negative controls are known samples used to validate the staining procedure. A positive control is a bacterium known to be Gram-positive, and a negative control is a bacterium known to be Gram-negative.
Using a positive control ensures that the staining reagents and procedure can correctly identify Gram-positive bacteria by showing the expected purple color.
Using a negative control ensures that the procedure can correctly identify Gram-negative bacteria by showing the expected pink/red color, confirming the decolorization step worked properly.
Together, these controls verify that the staining process is functioning correctly and help avoid misinterpretation of unknown samples due to procedural errors.
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