Group B streptococci (GBS) are the most common cause of neonatal sepsis, pneumonia, and meningitis. The alpha C protein is a surface-associated antigen; the gene (bca)
Group B streptococci (GBS) cause the majority of cases of neonatal sepsis and meningitis in the United States. Immunization of women of childbearing age is one strategy under consideration for the prevention of neonatal disease. The beta C protein, a 130-kDa antigen present in many clinical isolates of GBS, was purified from GBS by extraction into sodium dodecyl sulfate (SDS)-containing buffer, preparative SDS-polyacrylamide gel electrophoresis, and electroelution. Purified beta C protein antigen (25 ag) with Freund's adjuvant was used to immunize rabbits. Rabbits developed enzyme-linked immunosorbent assay titers of >1:1.6 x 106, and sera from immunized rabbits were administered to pregnant mice. Their neonatal pups were then challenged with a strain of GBS expressing beta C protein; 68% of these pups were protected by immune antiserum, whereas no controls were protected (P < 0.001). The immune serum (diluted 1:100) facilitated opsonophagocytic killing of GBS strains expressing the beta C protein but not those that do not express the antigen (mean log kill ± standard deviation = 0.71 ± 0.8 log1o CFU for beta' strains and 0.09 ± 0.2 for beta-strains; P = 0.02). In subsequent experiments, adult female mice were actively immunized with two e ises of 2, 5, or 10 ,ug of beta C protein 2 months prior to mating. One-to two-day-old offspring of these dam, were challenged with GBS and were protected in a dose-dependent manner, with 96% survival in the high-dose (10-tag) group and
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