Background:
Streptococcus agalactiae (group B streptococcus; GBS) is an important human pathogen causing pneumonia, sepsis and meningitis in neonates, as well as infections in pregnant women, immunocompromised individuals, and the elderly. For the future control of GBS-inflicted disease, GBS surface-exposed proteins are particularly relevant as they may act as antigens for vaccine development and/or as serosubtype markers in epidemiological settings. Even so, the genes encoding some of the surface proteins established as serosubtype markers by antibody-based methods are still unknown.
Methods:
We analyzed 140 clinical GBS strains from the Norwegian GBS reference laboratory. These strains were previously characterized for R3 expression by using a monoclonal R3 antibody. We typed the strains for presence/absence of sar5 using PCR, and some strains were also subjected to whole genome sequencing. Furthermore, we experimentally induced sar5 protein expression in a sar5 negative bacterial species followed by R3 protein detection by western analysis.
Results:
Nine of the 140 clinical GBS strains were sar5 positive by PCR, and the monoclonal R3 antibody recognized the sar5 gene product.
Conclusions:
We identify sar5 as the gene encoding the R3 surface protein.