Bacterial pathogens cause a wide spectrum of diseases in human and other animals. Some virulence factors, which are referred to as effectors, are directly translocated into the host cell via an injection apparatus, i.e., the type-III secretion system. Most effectors mimic host molecules, and translocated effectors are thereby able to perturb or modulate host cell signaling, cytoskeletal rearrangement, vesicular traffic, and autophagy, thus eliciting disease. Effectors are roughly classified among exotoxins, but in most cases, their functions are exerted focally when they are translocated into the host cell.