Gram’s iodine

Definition

Gram's iodine is a mordant used during the Gram staining procedure. It forms a complex with crystal violet dye, enhancing its retention in bacterial cell walls.

5 Must Know Facts For Your Next Test

1. Gram's iodine is applied after the crystal violet stain in the Gram staining process.
2. It helps to fix the crystal violet dye into the bacterial cell wall by forming a crystal violet-iodine complex.
3. Cells that retain the crystal violet-iodine complex appear purple and are classified as Gram-positive.
4. Cells that do not retain this complex and take up the counterstain (usually safranin) appear pink and are classified as Gram-negative.
5. The presence of Gram's iodine allows for differentiation between two major types of bacteria based on their cell wall structure.

Review Questions

Related terms

Crystal Violet:

A primary stain used in Gram staining that initially colors all cells purple.

Safranin:

A counterstain used in Gram staining that colors cells pink or red, allowing for differentiation of Gram-negative bacteria.

Mordant:

A substance used to set or stabilize stains or dyes, such as Gram's iodine in the context of microbiology.