Diversity
The capsule is found most commonly among Gram-negative bacteria:
- Escherichia coli (in some strains)
- Klebsiella pneumoniae
- Haemophilus influenzae
- Pseudomonas aeruginosa (more accurately described as a slime layer)
- Salmonella
However, some Gram-positive bacteria may also have a capsule:
- Bacillus megaterium for example, synthesizes a capsule composed of polypeptide and polysaccharides.
- Streptococcus pyogenes synthesizes a hyaluronic acid capsule.
- Streptococcus pneumoniae
- Streptococcus agalactiae produces a polysaccharide capsule of nine antigenic types that all contain sialic acid (Ia, Ib, II, III, IV, V, VI, VII, VIII).
- Staphylococcus epidermidis
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.
Read more about this topic: Bacterial Capsule
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