Opsonization of group B Streptococcus type III: studies using clinical strains and maternal sera

Luminol-dependent phagocytic chemiluminescence was used to measure opsonins to group B Streptococcus type III in serum samples from pregnant women. Mean levels were similar amongst patients colonized with this organism and those who were not. Values remained fairly constant for individual women during pregnancy apart from a small, but consistant fall in cord blood samples. Again using luminol-dependent chemiluminescence, 54 clinical isolates of group B Streptococcus type III were evaluated for susceptibility to serum opsonization. Six were found to be resistant and these originated from both colonized babies and babies with systemic GBS infections. Further studies demonstrated strain-to-strain variation in the degree of dependence on both heat-labile and heat-stable opsonins.