WANI Dictionary

Gram staining

The Gram staining is a differential staining method used to distinguish between two major groups of bacteria (Gram-positive and Gram-negative) based on differences in the composition of their cell walls.

This staining involves five steps:

1. The bacteria are fixed to a slide.
2. The slide is stained with crystal violet, a basic dye that stains all bacteria.
3. The slide is treated with iodine, which forms complexes with the crystal violet and helps to lock the dye within the cell walls.
4. The slide is washed with alcohol or acetone, which either removes the dye from the thin peptidoglycan layer of the Gram-negative bacteria or dehydrates the thick peptidoglycan layer of the Gram-positive bacteria, causing them to retain the crystal violet-iodine com-plex.
5. The slide is counterstained with a contrasting stain, such as safranin or fuchsin, which stains the Gram-negative bacteria pink or red, while the Gram-positive bacteria remain purple.

This staining technique is an important tool in microbiology, as it can help identify the type of bacteria present in a sample, which can aid in diagnosis and treatment of bacterial infections.

Definitions in the literature