The emergence of the group B streptococci as significant and prevalent agents in human perinatal and neonatal infections

The emergence of the group B streptococci as significant and prevalent agents in human perinatal and neonatal infections is relatively recent (1) and has stimulated renewed interest in the biology of these organisms. However, their antigenic composition has been studied for several decades. Shortly after characterizing this serological group of streptococci (2), Lancefield identified three distinctive serotypes, I, II, and III, on the basis of specific carbohydrate (CHO) ~ antigens (3) and subsequently separated type I into Ia and Ib (4). Recently, Wilkinson and her associates have identified a third member of the type I complex, type Ic, which is related to type Ia by the mutual possession of IaCHO and to type Ib by the presence in both of Ibc protein (5, 6). All three type I serotypes share IabcCHO (7). Other cellular antigens of the group B streptococci have been defined, (8) and some have been isolated and analyzed by immunochemical techniques (9-13). This paper summarizes a series of experiments that were designed to develop a quantitative assay of phagocytosis and to identify the critical microbial antigens and serum requirements for the opsonization of group B streptococci. This report deals with streptococci of types Ia, Ib, and Ic and, to facilitate the presentation and discussion of data, Table I summarizes the principal cellular antigens of these serotypes, as defined in the laboratories of Lancefield et al. (7) and of Wilkinson and Eagon (6).