A major function of a bacterium’s capsule is protection , especially from the host immune system and from drying out.

Quick Scoop

  • The capsule helps bacteria avoid being eaten by immune cells (it inhibits phagocytosis and reduces complement-mediated killing), which makes them more able to cause disease.
  • It protects the cell from desiccation because it is highly hydrated and holds water around the bacterium.
  • It helps bacteria stick to surfaces and to each other, aiding colonization and biofilm formation on tissues and medical devices.

In many exam-style questions that ask “What is a function of a bacterium’s capsule?” with options like propulsion, protection, DNA storage, or protein synthesis, the correct choice is protection.

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