Question

a. this image could be explained by leaving safranin dye on the smear for too long, causing all cells to wash out the purple color.
b. this image could be explained by leaving the primary stain step on the smear for too long, causing all cells to absorb the red color.
c. this image could be explained by omission of the decolorizing step, leading all cells to appear gram-negative.
d. this image could be explained by omission of the grams iodine step, causing all cells to appear gram-negative.

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 perform the safranin step. which of the following statements would correctly describe what you would see?

a. gram-negative organisms might not be visible.
b. you would not be able to view any organisms on the slide.
c. gram-negative organisms might incorrectly stain purple.
d. gram-positive organisms might incorrectly stain red.

Explanation:

Analyze the first question regarding the red-stained microscopic image

The microscopic image shows only red (Gram-negative appearing) rod-shaped and spherical bacteria. The selected option is D: "This image could be explained by omission of the Gram's iodine step, causing all cells to appear gram-negative." Without the mordant (Gram's iodine), the crystal violet-iodine complex does not form inside the thick peptidoglycan layer of Gram-positive cells. Consequently, the primary stain is easily washed out during the decolorization step, and all cells are counterstained red by safranin.

Analyze the second question regarding the omission of the safranin step

The second question asks what would be observed if the safranin counterstaining step is omitted when staining a mixed sample of Gram-positive and Gram-negative bacteria. Gram-positive bacteria will retain the crystal violet-iodine complex and appear purple. Gram-negative bacteria, which lose the primary stain during decolorization, require the safranin counterstain to become visible. Without safranin, these decolorized Gram-negative cells remain colorless and thus might not be visible under the microscope. This corresponds to option A.

Answer:

Question 1

• A. This image could be explained by leaving safranin dye on the smear for too long, causing all cells to wash out the purple color.
• B. This image could be explained by leaving the primary stain step on the smear for too long, causing all cells to absorb the red color.
• C. This image could be explained by omission of the decolorizing step, leading all cells to appear gram-negative.
• D. This image could be explained by omission of the Gram's iodine step, causing all cells to appear gram-negative. (Correct answer)

Question 2

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