The Role of the Group B Streptococcus Type VII Secretion System in Polymicrobial Environments

PROJECT SUMMARY Group B Streptococcus (Streptococcus agalactiae, GBS) is a Gram-positive, β-hemolytic bacterium and a leading etiologic agent of neonatal bacterial meningitis and major opportunistic pathogen in neonatal, pregnant, elderly, and diabetic populations. During pregnancy, GBS asymptomatically colonizes the vaginal tract of 30% of healthy women but can result in adverse pregnancy outcomes and severe neonatal disease. GBS is also increasingly isolated from adult diabetic wound infections. Both the vaginal tract and diabetic wound are complex polymicrobial environments. However, despite the public health burden of GBS, little is known about how GBS competes with these diverse populations to establish a niche and persist in either host environment. The Type VII Secretion System (T7SS) in Firmicutes secretes diverse toxic effectors that play an important role in interbacterial competition and virulence. Prior work from our laboratory has shown that the GBS T7SS contributes to cytotoxicity and virulence during meningitis as well as persistence in the murine vaginal tract during colonization. However, the specific mechanisms by which the GBS T7SS contributes to colonization as well as its role in other host environments remain unknown. My preliminary data indicate that the GBS T7SS inhibits growth of the important vaginal pathobiont and diabetic wound pathogen Enterococcus faecalis in vitro and in vivo in the murine vaginal tract. Additionally, I have found that a T7SS-associated LXG protein is a putative intracellular toxin that inhibits growth of E. coli and is important for persistence in the murine vaginal tract and diabetic wounds. Based on this, I hypothesize that the GBS T7SS mediates competition with neighboring bacteria in the vaginal tract and diabetic wound and may be mediated by a secreted LXG toxin with nuclease activity. This proposal seeks to evaluate the interaction of T7SS with the native vaginal microbiota in GBS colonization of the vaginal tract, interrogate the role of a T7SS-associated toxin in interbacterial competition, and elucidate the importance of GBS T7SS to diabetic wound infection. These goals will be addressed in vitro and in in vivo murine models of vaginal colonization and diabetic wound infection in the following specific aims: Aim 1: Characterize the importance of T7SS to GBS interbacterial competition and vaginal colonization. Aim 2: Evaluate function of a GBS LXG toxin and its contribution to T7SS interbacterial competition. Aim 3: Investigate the role of GBS T7SS in diabetic wound persistence.