Bacterial capsular polysaccharide (CPS)

Bacterial capsular polysaccharide (CPS) is a high-molecular-weight, extracellular carbohydrate polymer that forms a discrete outer layer (capsule) on the surface of many bacteria, both Gram-negative and Gram-positive[9][5]. CPS serves as a critical virulence factor, cloaking the cell to provide protection from host immune mechanisms such as phagocytosis and complement activation, as well as providing resistance to bacteriophages, desiccation, and antibiotics[3][5][8]. The chemical structure of CPS is highly diverse, with different species and strains producing unique repeat-unit polymers, often referenced by serotype[3][6]. CPS biosynthesis relies on dedicated pathways (Wzy-dependent, ABC transporter-dependent, synthase-dependent), and the capsule can be covalently anchored to the cell envelope[5][1]. CPS is a validated target for antibacterial therapies—most notably as the antigenic component in successful conjugate vaccines and (experimentally) the target for monoclonal antibodies or phage therapies[2][6]. However, the extensive structural heterogeneity and adaptability of capsule expression present substantial challenges to universal therapeutic exploitation[3][6][8].

Other names

capsulebacterial capsulecapsular polysaccharideK-antigen

Antibodies bind to CPS, promoting opsonization and clearance by immune cells[2][6]. Vaccines induce protective immunity (opsonic antibodies) targeting the capsule[2][6]. Bacteriophages recognize and degrade capsule polysaccharide to infect bacteria[6]. Novel non-biocidal polysaccharides interfere with biofilm formation[7].