Serotype markers in a Streptococcus agalactiae strain collection from Zimbabwe

Objective: Group B streptococci (GBS) from Southern African areas have been less well characterized. Our objective was to study serotype and serovariant distribution of carrier GBS strains as part of a study of the epidemiology of GBS carriage in pregnant women from Zimbabwe. Materials and Methods: We studied GBS isolated from 121 healthy pregnant women living in Harare and surrounding areas, Zimbabwe. Capsular polysaccharide (CPS) testing for serotype determination and surface-anchored protein testing for serosubtype determination were done by gene-based serotyping (PCR), except for the proteins R3 and a novel protein called Z, which were detected by antibody-based methods. Results: Strains of the CPS types Ia (15.7%), Ib (11.6%), II (8.3%), III (38.8%), V (24.0%) and NT (1.7%) were detected along with the strain-variable proteins Cί (15.7% of isolates), Cα (19.8%), Alp1 (epsilon-22.3%), Alp3 (5.0%), R4/Rib (46.3%), R3 (27.3%), Z (27.3%), and SAR5 (28.9%), which encodes the R5 protein. Up to four of the protein genes could be possessed or the gene product expressed by one and the same isolate. A total of 32 serovariants were detected. The findings assessed by us as most important were the very low prevalence of the gene Alp3 (Alp3 - 4.9%), high prevalence of R4 (Rib - 46.2%), the proteins R3 (27.3%), Z (27.3%), and of SAR5 (R5 - 28.9%). The low prevalence of Alp3, notably in GBS type V strains, differed from findings with CPS type V GBS from non-African areas. Bacteria of the various CPS types showed distinct CPS/protein-marker associations. Conclusion: The results are of importance in relation to regional variations of GBS phenotypes and genotypes and thus, of importance in planning and research in the context of future vaccine formulations