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Questions and Answers
What is the primary purpose of Gram staining?
What is the primary purpose of Gram staining?
- To identify the metabolic activity of bacteria
- To assess bacterial growth rate
- To determine the age of bacteria
- To classify bacteria into two groups based on their cell wall properties (correct)
What is the first step in the Gram staining procedure?
What is the first step in the Gram staining procedure?
- Rinse the slide with water
- Cover with Gram's iodine mordant
- Flood with safranin
- Prepare a heat-fixed smear of the bacteria (correct)
What color do Gram positive organisms appear after Gram staining?
What color do Gram positive organisms appear after Gram staining?
- Pink to red
- Blue to purple (correct)
- Green to yellow
- Colorless
Which solution is used as a mordant in the Gram staining process?
Which solution is used as a mordant in the Gram staining process?
During the decolorization step, what can happen if ethanol is applied for too long?
During the decolorization step, what can happen if ethanol is applied for too long?
How long should safranin typically be left on during the Gram staining process?
How long should safranin typically be left on during the Gram staining process?
What is a key characteristic of Gram negative bacteria in the Gram staining procedure?
What is a key characteristic of Gram negative bacteria in the Gram staining procedure?
What should be done to the slide after applying the final stain?
What should be done to the slide after applying the final stain?
Which step of the Gram staining process helps to determine if the crystal violet is still present on the slide?
Which step of the Gram staining process helps to determine if the crystal violet is still present on the slide?
Flashcards
What is Gram staining?
What is Gram staining?
A staining technique that differentiates bacteria based on the chemical & physical properties of their cell walls.
Gram-positive bacteria
Gram-positive bacteria
Gram-positive bacteria have thicker cell walls with a high peptidoglycan content, which retains the crystal violet stain even after decolorization.
Gram-negative bacteria
Gram-negative bacteria
Gram-negative bacteria have thinner cell walls with less peptidoglycan, allowing the crystal violet to be washed out during decolorization.
What is Gram's iodine mordant?
What is Gram's iodine mordant?
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What is the purpose of decolorization in Gram staining?
What is the purpose of decolorization in Gram staining?
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What is the role of the counterstain, safranin, in Gram staining?
What is the role of the counterstain, safranin, in Gram staining?
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What is a heat-fixed smear?
What is a heat-fixed smear?
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What is oil immersion?
What is oil immersion?
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Why is Gram staining a valuable tool in clinical and research settings?
Why is Gram staining a valuable tool in clinical and research settings?
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Study Notes
Gram Staining
- Gram staining is a crucial method for classifying bacteria into Gram-positive or Gram-negative groups.
- It relies on differences in cell wall structure.
- This technique is frequently used as the initial step in bacterial identification.
- However, not all bacteria are definitively identifiable using this method.
Gram Staining Procedure
- Preparation: Begin by creating a heat-fixed smear of the bacterial sample.
- Crystal Violet: Flood the smear with crystal violet for 30 seconds.
- Rinse: Rinse with water.
- Gram's Iodine: Apply Gram's iodine mordant for 1 minute.
- Rinse: Rinse with water.
- Decolorization: Decolorize using 95% ethanol (15-30 seconds, dropwise until crystal violet no longer washes off) or a 3:1 isopropanol-acetone mixture (30-60 seconds).
- Rinse: Rinse with water.
- Counterstain (Safranin): Stain with safranin (60-80 seconds; staining time varies between batches).
- Rinse: Rinse with water.
- Observation: Blot dry and examine under oil immersion.
- Results: Gram-positive bacteria appear blue-purple; Gram-negative bacteria appear pink-red.
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