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K. pneumoniae CPS
K. pneumoniae CPS Full Name
Klebsiella pneumoniae capsule polysaccharide
K. pneumoniae CPS Introduction
The capsular polysaccharide (CPS) of Klebsiella pneumoniae is a major virulence factor that forms a thick, hydrophilic layer surrounding the bacterial cell, providing protection against phagocytosis, complement-mediated killing, and antimicrobial peptides while contributing to biofilm formation and immune evasion. Over 80 capsular (K) types have been identified based on the structural and antigenic diversity of CPS, with serotyping historically performed using antisera raised against reference strains representing each K type. The capsule is composed of repeating oligosaccharide units containing various sugars (glucose, galactose, mannose, rhamnose, fucose, glucuronic acid, and others) linked in type-specific configurations, with the genetic determinants for capsule biosynthesis encoded in the chromosomal cps locus. Certain K types, particularly K1 and K2, are associated with hypervirulent strains that cause community-acquired invasive infections, including pyogenic liver abscesses, endophthalmitis, and meningitis, predominantly reported in Asia but increasingly recognized worldwide. The hypermucoviscosity phenotype, assessed by the string test, correlates with enhanced capsule production and is a hallmark of hypervirulent K. pneumoniae (hvKp) strains.
The genetic basis of CPS biosynthesis in K. pneumoniae involves a chromosomal capsule locus (cps cluster) containing genes for polysaccharide synthesis, modification, and export. The cps locus exhibits a conserved organization with genes encoding regulatory proteins (RmpA, RmpA2), transport machinery (Wzx flippase, Wzy polymerase, Wzc/Wzb export system), and type-specific glycosyltransferases and sugar biosynthesis enzymes. Comparative genomic analyses have revealed extensive diversity in capsule locus organization among different K types, with evidence of horizontal gene transfer, recombination, and gene conversion contributing to capsular switching and the emergence of novel serotypes. The wzi gene, encoding an outer membrane protein involved in capsule attachment to the cell surface, has been used for molecular capsule typing (wzi sequencing) as an alternative to traditional serological methods, enabling rapid identification of K types without the need for antisera. Whole-genome sequencing and bioinformatic analysis of cps loci have further enhanced capsule typing capabilities and revealed the evolutionary dynamics of capsule diversity in K. pneumoniae.
The CPS represents both a virulence determinant and a potential vaccine target for K. pneumoniae. The protective role of the capsule against host defenses makes it an attractive target for immunological intervention, and conjugate vaccines incorporating CPS antigens from prevalent K types have been explored as strategies for preventing K. pneumoniae infections, particularly in high-risk populations such as hospitalized patients, immunocompromised individuals, and those undergoing invasive procedures. However, the antigenic diversity of CPS, with over 80 K types, presents challenges for vaccine development, as a multivalent vaccine would need to include numerous serotypes to provide broad coverage. The emergence of hypervirulent strains with novel capsule types and the potential for capsular switching further complicate vaccine design. Alternative approaches have explored conserved subcapsular antigens, including outer membrane proteins, fimbriae, and LPS O-antigens, as vaccine candidates that could provide serotype-independent protection. Understanding the structure, biosynthesis, regulation, and immunobiology of K. pneumoniae CPS remains essential for developing effective prevention strategies against this increasingly problematic pathogen.
Alternate Names for K. pneumoniae CPS
Klebsiella pneumoniae; K. pneumoniae; K. pneumoniae capsule polysaccharide; K. pneumoniae CPS; K. pneumoniae K1 CPS; Capsule polysaccharide; CPS
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