Bacterial Capsule

It is a type of Glycocalyx. It is usually made of simple sugar residues. Bacillus anthracis has a Capsule made of amino acids.

Capsule is visualised under light microscope using 2 techniques

1. India Ink stain: It is not taken up by capsule - therefore capsule appears as a transparent halo around the cell, This stain is not used to visualise bacterial capsule but for visualising capsule of fungus Cryptococcus.
2. Quellung Reaction: The culture containing bacteria is mixed with antibodies specifically against the capsule. Capsule swells up making it easy to visualise.

See also Opsonization