In negative staining, which of the following is a typical step?

In negative staining, which of the following is a typical step?

• A. Heat fixing the slide
• B. Applying nigrosin to the slide
• C. Drying the slide by heating
• D. Rinsing with water

Answer: (B)

Negative staining relies on coloring the background with an acidic dye rather than staining the cells themselves. The dye used is nigrosin, which is negatively charged and is repelled by the negatively charged bacterial surface, so the cells remain colorless while the background becomes dark. This preserves cell morphology without heat-fixing. A typical step is applying nigrosin to the slide together with a small amount of bacterial suspension, forming a thin smear that is allowed to air-dry. Heat fixing is avoided because it can distort cells and any delicate structures, and rinsing with water is not part of the standard protocol since it would wash away the stain and the sample. Drying by heating is not used; instead the preparation is air-dried.

Negative staining relies on coloring the background with an acidic dye rather than staining the cells themselves. The dye used is nigrosin, which is negatively charged and is repelled by the negatively charged bacterial surface, so the cells remain colorless while the background becomes dark. This preserves cell morphology without heat-fixing. A typical step is applying nigrosin to the slide together with a small amount of bacterial suspension, forming a thin smear that is allowed to air-dry. Heat fixing is avoided because it can distort cells and any delicate structures, and rinsing with water is not part of the standard protocol since it would wash away the stain and the sample. Drying by heating is not used; instead the preparation is air-dried.