The present invention encompasses recombinant bacteria suitable for live attenuated vaccines, and methods of use thereof. One aspect of the present invention encompasses a recombinant Salmonella bacterium. The bacterium comprises a first promoter operably linked to a nucleic acid encoding a toxin and a second promoter operably linked to a nucleic acid encoding an antitoxin, wherein the second promoter is inactive in vivo, but active in vitro.
