Virulence properties of type VII Streptococcus agalactiae (group B streptococci) and immunochemical analysis of capsular type polysaccharide

Strains of a new polysaccharide type of group B streptococci (GBS), type VI I, have been isolated from human carriers and invasive infections. Some of these strains bear the protein antigen c or R, as do other GBS serotypes. T he capsular type polysaccharide is sialylated and this residue is involved in the immunodeterminant structure. All type VII strains examined were viru lent in CD-1 mice; the LD50 after intraperitoneal (i.p.) challenge was 4.57 (SD 0.12) x 10(7) cfu for the :reference strain and 5.49 (SD 1.5) x 10(7) cfu for clinical isolates. A particular feature of this serotype was the ab ility to induce septic arthritis not only when injected intravenously (i.v. ), but also when injected i.p. Rabbit antiserum against the capsular type V II polysaccharide exhibited opsonic activity in a phagocytosis assay and pr otective activity against infection.