Bacterial capsule

A well-organized layer of polysaccharides or proteins surrounding some bacterial cells. It can limit desiccation and help bacteria evade host defenses.

Phagocytosis: A cellular process that engulfs particles, including microbes, into membrane-bound compartments. Capsules can make bacterial cells harder for phagocytes to engulf.
Exopolysaccharide: A polysaccharide secreted by microorganisms that forms part of their extracellular environment. Many bacterial capsules are organized layers of extracellular polysaccharide.
Pneumococcal conjugate vaccine: A vaccine that links selected Streptococcus pneumoniae capsular polysaccharides to carrier proteins. It trains immunity against capsule types responsible for pneumococcal disease.
Streptococcus pneumoniae: A Gram-positive bacterium that causes pneumonia, meningitis, and other infections. Its polysaccharide capsule is a major determinant of virulence and vaccine targeting.
Slime layer: A loosely organized extracellular coating produced by some bacteria. Unlike a capsule, a slime layer is diffuse and less firmly attached to the cell.
Opsonization: The coating of a pathogen with molecules that promote its recognition and uptake by phagocytes. Capsular surfaces can hinder antibodies and complement from marking bacteria for uptake.
Capsular polysaccharide: A polysaccharide that forms or contributes to a bacterial capsule. It is the main capsule material in many medically important bacteria.
Meningococcal vaccine: A vaccine that protects against disease caused by Neisseria meningitidis, often by targeting capsular antigens. Capsular serogroups are central targets for several meningococcal vaccines.
Neisseria meningitidis: A Gram-negative bacterium that can cause meningitis and bloodstream infection. Its polysaccharide capsule helps it survive in the bloodstream.
S layer: A two-dimensional crystalline protein or glycoprotein layer on the surface of many bacteria and archaea. An S layer is an ordered surface lattice, not the hydrated capsule matrix.

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