The Mystery of Congo Red Staining Revealed

What does a clear halo around a cell indicate when bacteria are stained with Congo red followed by Crystal Violet?

The presence of a clear halo around a bacterial cell stained with Congo red followed by Crystal Violet indicates the presence of a capsule around the cell.

When bacteria are stained with Congo red followed by Crystal Violet, the clear halo around a cell indicates the presence of a capsule. The capsule is a protective layer made up of polysaccharides that surrounds the bacterial cell, lying outside of the cell envelope.

The capsule plays a crucial role in protecting the bacterial cells from toxic substances and preventing their desiccation. Additionally, the capsule helps the cells in adhesion to surfaces or other bacterial cells, aiding in their survival and interaction with the environment.

Congo red is a type of stain used for the qualitative detection of amyloids in cells. It colors the cells in a pink or mild red shade. Congo red is classified as an azo dye, being water-soluble and having high solubility in organic solvents.