Question

you are gram staining a known sample that contains both gram-positive and gram-negative bacteria. after you complete the staining, you realize that you performed the decolorizer step for 10 minutes instead of 10 seconds! which of the following statements would correctly describe what you would see?

a. you would not be able to view any organisms on the slide.
b. all organisms would appear some shade of blue.
c. gram-positive organisms might incorrectly stain red.
d. gram-negative organisms might incorrectly stain purple.

you are gram staining a known sample that contains both gram-positive and gram-negative bacteria. after you complete the staining, you realize that you did not use the alcohol bottle at all. which cells would appear purple? select all that apply.

a. gram-positive cells
b. no cells would show purple color
c. gram-negative cells

Explanation:

Analyze over-decolorization in Gram staining

Over-decolorizing (10 minutes instead of 10 seconds) washes out the crystal violet-iodine complex from both Gram-negative and Gram-positive cell walls. Consequently, Gram-positive cells lose their purple color and take up the counterstain (safranin), incorrectly staining red/pink.

Analyze omission of the decolorizer step

Omitting the decolorizer (alcohol) entirely means the crystal violet-iodine complex is never washed out from any cells. Therefore, both Gram-positive and Gram-negative cells retain the primary dye and appear purple.

Answer:

Question 1

• A. You would not be able to view any organisms on the slide.
• B. All organisms would appear some shade of blue.
• C. Gram-positive organisms might incorrectly stain red. (Correct answer)
• D. Gram-negative organisms might incorrectly stain purple.

Question 2

• A. Gram-positive cells (Correct answer)
• B. No cells would show purple color
• C. Gram-negative cells (Correct answer)