Step 1: Primary Staining

Use basic dyes such as crystal violet to stain the bacteria.

Step 2: Mordant Application

Apply iodine to fix the dye to the bacterial cell wall.

Step 3: Decolorization

Use acetone or ethanol to wash out the dye from Gram-negative bacteria.

Step 4: Counterstaining

Apply a red counterstain (safranin) to Gram-negative bacteria.

Gram-positive bacteria

Retain the violet dye and appear purple due to their thick cell wall.

Gram-negative bacteria

Take the red counterstain and appear red due to a thinner cell wall.