The present invention relates to isolated nucleic acid molecules encoding an autoinducer inactivation protein, wherein the encoded protein comprises an amino acid sequence selected from the group consisting of 104HXHXDH109~60aa~H169~21aa~D191 and 103HXHXDH108~72aa~H180~21aa~D202, and to expression vectors and transformed plant and animal cells comprising the same. The proteins encoded by these nucleic acid molecules provide to a susceptible plant or animal increased resistance to a disease the virulence of which is regulated by autoinducers. Also provided are methods of increasing disease resistance in susceptible plants and animals.