Strain specificity of opsonins for group B streptococci types II and III.

Strains of types II and III group B streptococci do not appear to be uniformly susceptible to opsonization by antibody-containing human sera, as studied using both a chemiluminescence and a radiolabeled bacterial uptake technique. We could not demonstrate a correlation of serum-sensitive or resistant strains with capsular antigen quantities, although serum absorption studies with whole organisms and HCl, trichloroacetic acid, and saline extracts indicated that the antibody to type-specific capsular polysaccharide is important in opsonizing both serum-resistant and serum-sensitive strains. Since trypsin treatment produced significantly enhanced opsonization of serum-resistant and serum-sensitive strains, proteins present on some group B streptococci may be important antiphagocytic factors.