Antigenic distribution of Streptococcus agalactiae isolates from pregnant women at Garankuwa hospital - South Africa.

INTRODUCTION: Streptococcus agalactiae (group B streptococcus; GBS) is globally recognised as one of the leading causes of neonatal sepsis and meningitis. It also causes adverse pregnancy outcomes such as stillbirth and miscarriages. Incidence of invasive disease is increasing in non-pregnant adults with underlying medical conditions (e.g., diabetes mellitus). Epidemiological studies of GBS infections are based on capsular serotyping. Genotyping of the surface anchored protein genes is also becoming an important tool for GBS studies. Currently ten different GBS serotypes have been identified. This study was performed to determine the prevalence of GBS capsular types (CTs) and surface anchored protein genes in isolates from colonized pregnant women attending antenatal clinic, at Dr George Mukhari Academic Hospital, Garankuwa, Pretoria, South Africa.

METHODS: The samples were collected over 11 months and cultured on selective media. GBS was identified using different morphological and biochemical tests. Capsular typing was done using latex agglutination test and conventional PCR. Multiplex PCR with specific primers was used to detect the surface anchored protein genes.

RESULTS: Of the 413 pregnant women recruited, 128 (30.9%) were colonized with GBS. The capsular polysaccharide (CPS) typing test showed that CPS type III (29.7%) was the most prevalent capsular type followed by CPS type Ia (25.8%), II (15.6%), IV (8.6%), V (10.9%) and Ib (8.6%); 0.7% of the isolates were nontypeable. Multiplex PCR revealed that the surface proteins genes were possessed by all the capsular types: rib (44.5%), bca (24.7%), alp2/3 (17.9%), epsilon (8.6%) and alp4 (4.7%).

CONCLUSION: The common capsular types found in this study are Ia, III, and II. The most common protein genes identified were rib and bca, and the distribution of the surface protein genes among the isolates of different capsular types showed similar trends to the distribution reported from previous studies.