Micro-indirect hemagglutination test for detection of antibodies to the Ibc protein of group B Streptococcus.

A micro-indirect hemagglutination test was developed for detecting antibody against the Ibc protein of group B Streptococcus. Formalin-preserved, tanned sheep erythrocytes were sensitized with a partially purified preparation of Ibc protein from a type Ic strain of group B streptococci. A total of 76% of 103 sera from pregnant and nonpregnant women had demonstrable antibody against this protein, with titers ranging from 10 to 320. Examination of five pairs of mother and cord sera revealed passive transfer of these antibiodies from mother to infant. This testing on a limited number of sera also revealed that elevated antibody titers against Ibc protein were more common among carriers of group B streptococci, especially those harboring strains with Ibc protein antigen, than among noncarriers. The technique described was found to be simple, specific, sensitive, and reproducible and may be of value in assessing the immune status of pregnant women as well as for epidemiological purposes.