<；P>；PROBLEM TO BE SOLVED: To provide a material for inhibiting autoinducer-2, and to provide a material effective for prevention and/or treatment of an infectious disease. <；P>；SOLUTION: The autoinducer-2 inhibitor includes a compound represented by formula I (wherein, R<；SP>；1<；/SP>；and R<；SP>；2<；/SP>；are each independently hydrogen, a hydroxy group, an aryl group or an alkoxy group, or form an oxo group by bonding to each other； R<；SP>；3<；/SP>；is a halogen； and R<；SP>；4<；/SP>；is hydrogen, an amino group or a halogen) or a salt thereof as an active ingredient. The agent for preventing and/or treating the infectious disease includes the compound or the salt thereof as an active ingredient. <；P>；COPYRIGHT: (C)2009,JPO&INPIT
