Which step can be omitted without affecting determination of Gram reaction?

Which step can be omitted without affecting determination of Gram reaction?

• A. The primary stain
• B. The mordant step
• C. The counterstain safranin
• D. The decolorizer step

Answer: (C)

Understanding Gram staining starts with how the differential color is produced. The key idea is that Gram reaction depends on whether the crystal violet–iodine complex is retained after the decolorization step. The primary stain colors all cells, and the mordant helps the crystal violet stay locked in the thick peptidoglycan of Gram-positive cells. The decolorizer then differentiates: it washes away the dye from Gram-negative cells, which have a thinner peptidoglycan layer. The counterstain with safranin provides color to the decolorized cells so you can see them clearly. If you omit the counterstain, Gram-positive cells remain purple while Gram-negative cells become colorless after decolorization. You can still distinguish the two groups based on that color difference, so the Gram reaction can be determined without the counterstain. The other steps are essential for establishing and exploiting the differential retention of dye.

Understanding Gram staining starts with how the differential color is produced. The key idea is that Gram reaction depends on whether the crystal violet–iodine complex is retained after the decolorization step. The primary stain colors all cells, and the mordant helps the crystal violet stay locked in the thick peptidoglycan of Gram-positive cells. The decolorizer then differentiates: it washes away the dye from Gram-negative cells, which have a thinner peptidoglycan layer. The counterstain with safranin provides color to the decolorized cells so you can see them clearly.

If you omit the counterstain, Gram-positive cells remain purple while Gram-negative cells become colorless after decolorization. You can still distinguish the two groups based on that color difference, so the Gram reaction can be determined without the counterstain. The other steps are essential for establishing and exploiting the differential retention of dye.