Purpose:
Group B Streptococcus (GBS) is a Gram positive coccus which is part of the normal microbiota of the GI and GU tracts. However GBS is also a major cause of septicaemia and meningitis in newborns. Colonisation with GBS during pregnancy is a major risk factor for neonatal infection. Intrapartum antibiotic prophylaxis has greatly reduced incidence of early onset disease. However concerns over emerging antibiotic resistance and its impact on neonatal intestinal microbiota and a lack of protection afforded by intrapartum antibiotics outside of the first few days of life have led to GBS becoming a candidate for maternal vaccine development. Maternal IgG antibodies targeting capsular polysaccharides have been observed to provide protection against disease (Fabbrini et al 2016). Establishing a serocorrelate of protection could assist in the pathway to licensure of a GBS vaccine.

Methods:
A Bill and Melinda Gates Foundation funded consortium led by Kirsty Le Doare to establish a standardised multiplex immunoassay (MIA), based up luminex’s Xmap technology, and an opsonophagocytic killing assay (OPkA). This will be followed by a inter laboratory study between multiple partners to establish assay parameters and reproducibility.

Results:
Standardised reagents (CPS-PLL conjugates, standards) are being developed and characterised and preparations are being made for the inter laboratory study.

Conclusion:
Identifying a level of IgG which provides protection from GBS disease has been hampered by a lack of assay standardisation. A consortium has been established to develop standardised reagents and assays, including the multiplex immunoassay. Future studies to assess the relationship between antibody level, colonisation and disease are being planned.