Serotype markers in a Streptococcus agalactiae strain collection from Zimbabwe

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.

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.

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.

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.