This invention provides a purified extracellular bacterial autoinducer-2 signaling molecule, the production of which is regulated by changes in environmental conditions associated with a shift from a free-living existence to a colonizing or pathogenic existence in a host organism. In one aspect, the interface apparatus includes a gesture sensor, a gesture processor, and a head-up display, where the gesture sensor and the gesture processor recognizes and interpret the information input by the user’s finger gesture and such information is displayed on the HUD. The mode change device includes an operation member that is operable by an operator.