Group B Streptococcus capsular polysaccharide serotype Ib (GBS CPS Ib)

The Group B Streptococcus capsular polysaccharide serotype Ib (GBS CPS Ib) is a high molecular weight polysaccharide that forms the bacterial capsule, serving as a major virulence factor enabling evasion of human innate immune defenses.[1][2][4][7] It consists of repeating pentasaccharide units with a disaccharide backbone of β-D-Glc p-(1→4)-β-D-Gal p and a trisaccharide side chain featuring β-D-Gal p-(1→3)-β-D-Glc p-NAc linked to the backbone, terminated by α-(2→3)-linked sialic acid (Neu p-NAc), distinguishing it from serotype Ia by the internal side chain linkage.[1][2] Encoded by the cps gene cluster with serotype-specific glycosyltransferases (e.g., CpsI, CpsJ) and polymerases, it shows structural similarity to types Ia and VI, likely arising from genetic recombination and horizontal gene transfer.[1] As a surface antigen, it is a key target for glycoconjugate vaccine development due to its role in immunogenicity and serologic specificity.[2][3][4]

Other names

Type Ib capsular polysaccharideIb CPSGBS type Ib polysaccharide