How will Escherichia coli appear in a Gram stain if the mordant (iodine) is not applied during the staining process?

• A. Green, due to a reaction between crystal violet and safranin
• B. Pink or red, because the crystal violet is not fixed and is washed out by alcohol
• C. Purple, because the crystal violet remains trapped in the cell wall
• D. Colorless, because all stains are washed away

Answer: (B)

Verified step by step guidance

1. Understand the role of the mordant (iodine) in the Gram staining process: iodine forms a complex with crystal violet dye inside the bacterial cell wall, which helps fix the dye and retain it during the decolorization step.
2. Recall that Escherichia coli is a Gram-negative bacterium, which normally appears pink or red after Gram staining because the crystal violet-iodine complex is washed out by alcohol, and the counterstain safranin stains the cells.
3. Consider what happens if iodine is not applied: without the mordant, the crystal violet dye is not fixed inside the cell wall, so it will be easily washed away during the alcohol decolorization step.
4. Since the crystal violet is washed out, the cells will not retain the purple color and will instead take up the counterstain safranin, which stains them pink or red.
5. Therefore, the expected appearance of Escherichia coli in a Gram stain without iodine is pink or red, because the crystal violet is not fixed and is washed out by alcohol.