What is the differential staining method that fixes bacteria to a slide, stains with crystal violet and iodine, then washes with alcohol and counterstains with safranin?

• A. Gram Stain
• B. Acid-fast stain
• C. Endospore stain
• D. Capsule stain

Answer: (A)

Differentiating bacteria by the structure of their cell walls using a Gram stain. In this method, crystal violet stains all cells purple, iodine acts as a mordant to fix the dye, an alcohol wash decolorizes cells with thinner peptidoglycan (Gram-negative) while thicker-walled Gram-positive cells stay purple, and a counterstain with safranin makes the decolorized cells appear pink or red. This sequence is specific to Gram staining, distinguishing Gram-positive from Gram-negative organisms. Other stains use different reagents and steps (acid-fast, endospore, capsule) and would not follow this exact procedure.