Streptococcus gallolyticus subsp. gallolyticus (Sgg) is implicated in life-threatening bacteremia, infective endocarditis (IE) and colorectal cancer (CRC). Despite its clinical importance, the underlying virulence mechanism of Sgg is poorly understood. Recent findings from our lab demonstrated that a type VII secretion system (T7SS) plays a significant role in Sgg virulence. In preliminary studies to further dissect the activities mediated by the T7SS, EsxA, a specific T7SS effector, was found to be crucial in influencing colonic epithelial homeostasis likely by targeting a host cell surface receptor of critical function. The goal of the parent R01 proposal is to further delineate the importance of EsxA in Sgg virulence and to elucidate its mechanism of action in colonic epithelial cells and animal models. This supplement proposal will further extend the studies proposed in the parent R01 to investigating the contribution of EsxA and other T7SSs in host immune responses to Sgg. Completion of the proposed studies is expected to shed light on the role of T7SS in host immune responses to Sgg and gain a more comprehensive view of the activities of Sgg T7SS across different host cell types. The results will further advance our understanding of Sgg virulence mechanism and T7SS functionality. The supplement proposal will also provide training for a student from an underrepresented group in the area of molecular pathogenesis and host-pathogen interactions. A career development and mentorship plan is provided and outlines training in research skills, graduate education, and career development with the goal of ensuring the candidate student to be a competitive and successful researcher in the future.