Low prevalence of the immunoglobulin-A-binding beta antigen of the C protein among Streptococcus agalactiae isolates causing neonatal sepsis

Streptococcus agalactiae (Group B streptococcus, GBS) is the most important pathogen causing neonatal sepsis. The role of bacterial proteins contribut ing to pathogenicity in GBS infections has not yet been clearly determined, but the C protein complex has been suggested to be involved in both virule nce and protective immunity. The aim of this study was to assess the preval ence of GBS strains bearing the gene encoding for the beta antigen of the C protein;among clinical isolates from 68 neonates with sepsis, 45 newborns colonized without clinical signs of infection, and 50 isolates from pregnan t women. The prevalence of the beta antigen gene in all three groups was lo w (22% vs. 19% vs. 22%), and the differences between groups were not statis tically significant. Clinical characteristics and cytokine plasma levels di d not differ between septic patients with beta antigen-positive and -negati ve strains. The beta-antigen gene was not found among serotype III isolates , which accounted for roughly half of all the strains isolated. Thus, polym erase chain reaction (PCR) analysis based on the beta antigen gene seems no t helpful for distinguishing invasive from colonizing GBS strains. A vaccin e based on peptide antigens from the beta antigen of the C protein would mo st probably not provide protection against the majority of GBS isolates. Wh en analyzing the PCF: products of the C protein beta antigen gene by DNA se quencing, a genetic heterogeneity was observed, revealing small repetitive genetic elements within the amplified fragment, an observation that should be studied further.