Klebsiella pneumoniae capsular polysaccharide antigen

The Klebsiella pneumoniae capsular polysaccharide antigen is a complex carbohydrate structure forming an external capsule around the bacterium. This capsule—also known as the K antigen—is one of two major surface antigens used to classify K. pneumoniae strains (the other being O-antigen). The capsule plays a critical role in virulence by protecting bacteria from phagocytosis and complement-mediated killing by host defenses, enabling survival during infection.[1][5] Over 77 distinct types have been identified globally.[5] Certain serotypes such as K1 and K2 are strongly associated with invasive disease. Because it is highly immunogenic when properly preserved, this molecule has become an important focus for vaccine development efforts against multidrug-resistant K. pneumoniae. Experimental conjugate vaccines using purified or enzymatically processed CPS from prevalent serotypes have shown strong protective effects in animal models by inducing robust anti-capsule antibody responses.[2] Additionally, phage-derived enzymes called depolymerases can degrade these capsules therapeutically. No direct small-molecule inhibitors exist for this target; however, its essential role in pathogenesis makes it an attractive candidate for both passive immunotherapy (antibodies) and active vaccination strategies aimed at preventing severe infections caused by Klebsiella species.[1][2]

Other names

K antigen (Klebsiella pneumoniae)Capsular polysaccharide (CPS) of Klebsiella pneumoniaeK. pneumoniae capsule antigenCapsule K-antigen

For investigational drugs/vaccines targeting this molecule: Induction of anti-capsule antibodies that promote opsonization and bactericidal activity by the host immune system. Phage depolymerases enzymatically degrade the capsule to expose bacteria to immune attack or antibiotics.