Plays a role in the bacterium-induced formation of multinucleated giant cell (MNGC), which is formed after host cell fusion, as well as in the intercellular spreading of bacteria and in the induction of apoptosis in macrophages. May act in concert with other effector proteins to induce fusion of host cell membranes. Secreted via the bsa type III secretion system, and probably inserted into host membranes. Human meliodoisis patients have detectable antibody response to BipB. However, BipB does not act as a protective antigen. Belongs to the invasin protein B family.