Bacteria can be classified into two groups on the basis of the differences in the cell envelopes and the manner in which they respond to the staining procedure developed by Gram viz., those that take up the gram stain are Gram positive and the others that do not are called Gram negative bacteria.

Gram staining is a method used to classify bacteria into two groups based on the characteristics of their cell walls. Here’s a breakdown of the Gram staining process, which is best visualized with a flowchart:

• Fixation: Bacteria are fixed to a slide by heat.
• Primary Stain: Crystal violet stain is applied.
• Mordant: Iodine solution is added to form a complex with crystal violet.
• Decolorization: Alcohol or acetone is used to wash the slide.
• Gram-positive bacteria retain the crystal violet-iodine complex and appear purple.
• Gram-negative bacteria lose the stain and become colorless.
• Counterstain: Safranin or fuchsine is applied.
• Gram-negative bacteria take up the counterstain and appear red or pink.