Klebsiella pneumoniae K1 capsular polysaccharide (K. pneumoniae K1 CPS)

Klebsiella pneumoniae K1 capsular polysaccharide is a high-molecular-weight, surface-exposed polysaccharide polymer and a major component of the mucoid capsule characteristic of hypervirulent K1 strains of K. pneumoniae.[1][3][6] The K1 capsule is composed of repeating trisaccharide units: (→3)-β-D-Glc-(1→4)-[2,3-(S)-pyruvate]-β-D-GlcA-(1→4)-α-L-Fuc-(1→), with unique modifications including pyruvylation of glucuronic acid and O-acetylation of fucose that are essential for its immunogenicity and virulence.[2][3][6] The capsule acts as a key virulence factor, protecting bacteria from phagocytosis, complement-mediated killing, and innate immune recognition, thus enabling survival in host tissues and contributing to the severity of infections such as pyogenic liver abscess, especially in immunocompromised hosts or those with diabetes.[1][5] The K1 CPS is highly immunogenic and is being targeted by experimental therapies, including phage-derived depolymerase enzymes and K1 CPS-based conjugate vaccines, both of which aim to strip the protective capsule and facilitate immune clearance of the pathogen.[2][3][6] Antigenic diversity and the tight specificity of immune responses to capsular polysaccharide serotypes remain challenges for therapeutic and prophylactic strategies.

Other names

K1 CPSK1 capsuleKlebsiella K1 capsuleK1 capsular antigen

Enzymatic depolymerization (via phage or recombinant capsule depolymerase) which removes the capsule and sensitizes bacteria to immune clearance[2][6] Vaccine-induced antibody targeting and opsonophagocytosis (for K1 CPS-based vaccines)[2][6]