Klebsiella pneumoniae K2 capsular polysaccharide (K2 CPS)

The Klebsiella pneumoniae K2 capsular polysaccharide is a highly mucoid, extracellular glycan matrix that constitutes the capsule of K2 serotype strains of Klebsiella pneumoniae, a major pathogen of bloodstream and severe systemic infections. The capsule is largely composed of repeating tetrasaccharide units, typically containing D-glucose, D-glucuronic acid, D-galactose, and D-rhamnose, with additional modifications such as O-acetylation being crucial for immunogenicity[1][2][4]. K2 capsule is one of the most virulent determinants among the defined >80 Klebsiella capsule types[5][6], helping bacteria evade both innate and adaptive immune responses by physically blocking recognition, inhibiting complement deposition, and preventing phagocytosis[8][9]. Its presence strongly correlates with disease severity and is associated with hypervirulent and multidrug-resistant strains[5][7]. The K2 capsule is a validated therapeutic target for vaccine and antibody-based interventions and is also currently under investigation for phage therapy using capsule-degrading enzymes (depolymerases)[1][3][6][7][10]. Capsule-based vaccines have demonstrated superior protection in preclinical models compared to O-antigen based alternatives, though effectiveness may be limited by capsular diversity and potential immune escape mechanisms[7].

Other names

K2 capsular polysaccharideK2 capsuleK antigen type K2

Enzymatic depolymerization of capsule using phage-derived proteins (tailspike depolymerases)[1][3]; Induction of antibody response via vaccine targeting K2 CPS to enable host immune recognition and killing[7][10]; Reduction of capsule-mediated serum resistance, restoring susceptibility to immune clearance[3]