The present invention encompasses a recombinant bacterium comprising a regulated rfaH nucleic acid, as well as a vaccine comprising said recombinant bacterium. Other embodiments of the present invention encompass a recombinant bacterium comprising a regulated rfaH nucleic acid and a regulated rfc nucleic acid, while additional embodiments encompass a recombinant bacterium comprising a regulated rfaH nucleic acid and at least one nucleic acid encoding at least one exogenous antigen.