Resveratrol (3,5,4'-trihydroxy-trans-stilbene), an antifungal phytoalexin produced by grapes, peanuts, and Japanese knotweeds, is thought to be a beneficial dietary phytochemical in red wine and grape juice. Information on its antibacterial properties and biotransformation, however, is limited. We surveyed the interactions of resveratrol with 43 strains of bacterial species that are often animal- or human-associated. Resveratrol at 50 mg L(-1) reduced the growth rates of most of the bacteria tested, but did not totally prevent growth even at much higher levels. Eleven of the 43 bacteria were capable of transforming at least 20% of the resveratrol. Three major metabolites were identified as resveratroloside, piceid, and dihydroresveratrol, and three other metabolites were partially characterized.