Capsule (microbiology)

The term capsule in microbiology refers to a layer that lies outside the cell wall of bacteria. This layer is well organized and not easily washed off. It is usually composed of polysaccharides, but could be composed of other materials. Capsules help protect bacteria against phagocytosis. Capsules also contain water which protects bacteria against desiccation. They also exclude bacterial viruses and most hydrophobic toxic materials such as detergents.