Streptococcus agalactiae, also called Group B streptococcus (GBS), is an organism that can cause severe diseases in susceptible hosts including newborns, pregnant women and the elderly. The female reproductive tract is a major reservoir for GBS, but little is known about the specific GBS factors that promote colonization and vaginal persistence. Bacterial surface-associated proteins, such as PilA and serine-rich repeat (Srr) protein, both contain a LPXTG cell-wall anchoring motif and have been shown to facilitate GBS interaction with host cells. In order to understand whether they play a similar role in the female reproductive tract, I examined in vitro models of GBS interaction with human vaginal and cervical epithelial cell lines. Analysis of mutant GBS strains deficient in cell surface proteins Srr and PilA demonstrated that these factors contribute to host cell attachment, but detailed mechanism is still unknown. It was recently determined that Srr1 possesses a fibrinogen-binding region (BR) with a flexible C-terminal extension (the "latch" domain), which can interact with fibrinogen via the "dock, lock, latch" (DLL) mechanism; this interaction promotes GBS attachment to brain endothelium and contributes to the development of meningitis. I hypothesized that GBS cervicovaginal colonization is mediated by the Srr1-fibrinogen interaction through the same DLL mechanism. In my study, I observed that the addition of exogenous fibrinogen enhanced wild-type GBS attachment, but not the Srr1 deficient mutant, to vaginal and cervical epithelium. Further a GBS mutant strain lacking only the Srr1 latch domain exhibited decreased binding ability in vitro and decreased vaginal persistence in an in vivo mouse model of GBS colonization. Moreover, purified Srr1-BR peptide bound directly to host cells, but with lower affinity when the latch domain was deleted. My data suggest that the latch domain of the Srr1 glycoprotein plays a crucial role in mediating GBS adherence to the female reproductive tract through the interaction with fibrinogen. It is known that GBS regulates gene expression of virulence factors, including those that bind fibrinogen, using the two-component regulatory system CovR (for control of virulence regulator). My data indicate that CovR plays a significant role in GBS vaginal adherence and invasion; continued studies of CovR and CovR-regulated factors will clarify how GBS modulates the host interaction, which is crucial to elucidate the switch from a normal vaginal inhabitant to an invasive pathogen.