>8)-Linked

We characterized the genetic defect of a capsule-deficient serogroup B meningococcal strain created by Tn916 mutagenesis. The transposon insertion interrupts a capsule biosynthesis gene, synX, which is involved in the production of N-acetyl-D-mannosamine, a precursor of the (a2-*8)-linked polysialic acid capsule of serogroup B meningococci. Capsular polysaccharide is a major virulence determinant of pathogenic bacteria (14). Encapsulated organisms are pro-tected from host defenses, including phagocytosis, opsoniza-tion, and complement-mediated killing (3). The capsule of serogroup B strains of Neisseria meningitidis, a major cause of invasive meningococcal disease, is composed of (ot2->8)-linked polysialic acid. The group B capsule shares biochemical and epitope identities with certain human cell glycoconjugates, such as the neural cell adhesion molecule (N-CAM) (6, 11). Part of the protection from host killing afforded by the group B capsule is due to its poor immunogenicity