Gram's stain is a four-step staining process used to separate bacteria into groups. Which option best describes it?

• A. A culture medium
• B. A four-step staining process used to separate bacteria into groups
• C. A virus
• D. A vaccine

Answer: (B)

Gram staining is a differential staining method that classifies bacteria into two groups based on their cell-wall structure. In the four-step process, a primary stain (crystal violet) is applied, iodine acts as a mordant, the slide is treated with a decolorizer, and a counterstain (safranin) is added. Bacteria with thick peptidoglycan walls retain the purple color and appear Gram-positive, while bacteria with thinner walls lose the purple during decolorization and appear pink as Gram-negative. This description matches the idea of a staining technique used to separate bacteria into groups. It isn’t a culture medium used to grow organisms, nor is it a virus or a vaccine.