| Summary: | Streptococcus agalactiae (Group B Streptococcus, GBS) is a cause of life-threatening infections in neonates and in the elderly. Clinical presentations of GBS disease include sepsis, pneumonia and meningitis. GBS normally resides as a commensal microorganism of the female genitourinary tract, where it can be vertically transmitted to the foetus/neonate in utero or during parturition. The oropharynx also represents an important point of entry for GBS in both neonates and adults. GBS is thus able to adhere to a variety of host tissues, including epithelia of the vagina, lung or meninges. These interactions are primarily mediated by cell surface proteins that recognise specific host receptors. This study investigated a family of putative GBS adhesins designated Group B streptococcal proteins (Bsp). Bsp proteins belong to the antigen I/II (AgI/II) polypeptide family, which are multifunctional adhesins found across the Streptococcus genus. It was hypothesised that Bsp proteins function as colonisation determinants of GBS. Bsp proteins were shown to promote binding to factors relevant to colonisation of vaginal or oral niches, including human vaginal epithelium, scavenger receptor glycoprotein-340 and to the resident microbiota member Candida albicans. Complementary structural characterisation of dissected domains of the prototypical Bsp family member, BspA, revealed structural features not previously reported in AgI/II family polypeptides. This suggested that the mechanism of Bsp-mediated receptor engagement might be distinct from that of other AgI/II family members. Collectively, the results of this study identified Bsp family proteins as novel adhesins that provide potential competitive advantage in GBS colonisation and pathogenesis. A better understanding of the molecular mechanisms involved in bacterial colonisation will assist development of new clinical interventions against GBS disease.
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