Typing of human isolates of Streptococcus agalactiae (group B streptococcus, GBS) strains from Zimbabwe.

Abstract

Serotyping and genotyping are important tools in epidemiological studies of group B streptococcal (GBS) infections, which are important diseases in man, particularly in newborns. In the present study, 241 GBS isolates from Zimbabwe, comprising 124 carrier isolates from pregnant women and 117 isolates from patients hospitalised for various diseases, were serotyped. Antibodies specific for the capsular polysaccharide antigens (CPAs) Ia, Ib and II-V and antibodies specific for the surface-localised proteins, c(alpha), c(beta), R1, R3 and R4 were used for serotyping. Strains of the CPA types Ia (17%), III (47.7%) and V (23.2%) predominated. Of the various protein antigens, c(alpha) and R4 were expressed with highest frequency, c(alpha) by 100% of the CPA type Ia strains and R4 by 92% of the CPA type III strains. The R3 protein occurred frequently (24%), especially in type V strains (84%). A total of 25 serovariants was detected in the strain collection with the variants Ia/c(alpha) (16%), III/R4 (43.5%) and V/c(alpha), R3 (14.1%) occurring with the highest frequency. Serotype and subtype distribution of the carrier isolates were essentially similar to those of the disease-associated isolates. Genomic heterogeneity was demonstrated by pulsed-field gel electrophoresis of type III/R4 and type V/c(alpha), R3 isolates, but to a much lesser extent than recorded with Norwegian strains. These results demonstrate that many variants of GBS occur in the Zimbabwean population. The data obtained may assist in the formulation of a possible future GBS vaccine for Zimbabwe and perhaps for other African countries.