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 .sup.104HXHXDH.sup.109.about.60aa.about.H.sup.169.about.21aa.about.D.sup.- 191 and .sup.103HXHXDH.sup.108.about.72aa.about.H.sup.180.about.21aa.about- .D.sup.202, 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.