Define Capsule Staining (Anthony Staining Method)?
A rigid, well-organized gelatinous layer called capsule is present outside the cell wall of many bacteria e.g. Streptococus pneumoniae, Clostridium perfringens and Klebsiella pneumoniae. It is mostly made up of polysaccharide (homo or hetero-polysaccharide) though in few it is proteinaceous in nature, e.g., in Bacillus anthracis it consists of poly-D-glutamic acid. The ability to form capsule is genetically determined. Capsule is not required for reproduction or growth of bacteria though it confers several advantages:
1. It protects the bacteria from phagocytosis by host phagocytes, so it contributes to the virulence of bacteria, e.g. Streptococcus pneumoniae.
2. It provides protection against dessication.
3. It helps the bacteria in attachment to host tissues e.g. in Streptococcus mutans capsule helps in attachment to the surface of the teeth and thus causing dental caries.
4. Capsule may be used as a source of nutrition by S. mutans.
5. Viscosity of a capsule may help in inhibiting the movement of nutrients out of the cell.
6. Capsule also exclude bacterial viruses and most hydrophobic toxic materials such as detergents.