Streptococcus pneumonia is a virulent pathogen which cause pneumonia in humans. The polysaccharide capsule plays an important role in the virulence of this bacteria.
This outer capsule do not allow immune cells like phagocytic cell to engulf and kill this bacteria because it cause slippery surface for phagocytes.
Capsule also allow this bacteria to escape from mucus because its capsule repels the mucus as it contain negative charge and capsule is responsible for invasive infection because it helps in colonization of bacteria in host. So by making capsule it avoid destruction by a phagocyte.
