capsule of nine antigenic types that all contain sialic acid (Ia, Ib, II, III, IV, V, VI, VII, VIII). Staphylococcus epidermidis Staphylococcus aureus Lactococcus garvieae synthesizes capsular gene clusters and some time synthesizes a hyaluronic acid capsule. The yeast Cryptococcus neoformans, though not a bacterium, has a similar capsule. Capsules too small to be seen with an ordinary microscope, such as the M protein of Streptococcus pyogenes, are called microcapsules. Demonstration of capsule India ink staining: the capsule appears as a clear halo around the bacterium as the ink can't penetrate the capsule. Maneval's capsule stain: the capsule appears as a clear halo between the pink-stained bacterium and the bluish-grey stained background. The background stain is the acidic stain Congo red (which changes color to bluish-grey due to the pH), and the pink stain is fuchsine. Serological methods: Capsular material is antigenic and can be demonstrated by mixing it with a specific anticapsular serum. When examined under the microscope, the capsule appears 'swollen' due to an increase in its refractivity. This phenomenon is the basis of quellung reaction. Use in vaccination Vaccination using capsular material is effective against some organisms (e.g., H. influenzae type b, S. pneumoniae, and N. meningitidis). However, polysaccharides are not highly antigenic, especially in children, so many capsular vaccines contain polysaccharides conjugated with protein carriers, such as the tetanus toxoid or diphtheria toxoid. This stimulates a much more robust immune response. See also Bacterial cell structure Quellung reaction, a method to visualize capsule under a microscope References Bacteriology