from Ana Rita Furtado and Agathe Subtil writing in Bacterial Pathogenesis: Molecular and Cellular Mechanisms:
Several intracellular bacteria survive and multiply inside membrane-bounded compartments called vacuoles. While this lifestyle offers several advantages against host cell defenses, it also imposes important constraints. Pathogens have developed independent strategies to survive within their host, and as a consequence, each "vacuole" is unique to a given bacterium in its composition and behavior. However, common requirements and strategies emerge. We describe how intracellular pathogens interact with the host trafficking pathways to transform their vacuole into a favorable niche, and undermine the host defense mechanisms against intruders. This is mainly achieved through the action of bacterial proteins translocated out of the vacuoles into the host cytoplasm. An increasing number of these "effector" proteins are currently being identified, and the functions of a few of them start to be understood.
Further reading: Bacterial Pathogenesis: Molecular and Cellular Mechanisms