Effects of some capsular components on pathogenicity of type IV and provisional type V group B streptococci

Recently, 2 new Group B Streptococcus (GBS) serotypes, IV and provisional V, have been described. To gain information on the relationship between pathogenicity and occurrence of some specific bacterial components, we studied the virulence in a mouse model, the ultrastructural aspect of type IV and V cells, and their sialic acid content. The new serotypes exhibited very low virulence for the mouse, similar to that found in GBS serotype III. The amount of sialic acid present on the bacterial surface (4.8 mg/g of bacterial cells in type IV and 1.8 mg/g in provisional type V) accorded well with this low virulence. When pretreated with type-specific antisera, a very thin and irregular layer of capsular material surrounded the cells in type IV, while a clearly defined capsule was observed in provisional type V.