Construction of Recombinant Attenuated Salmonella enterica

Recombinant bacterial vaccines must be safe, efficacious, and well tolerated, especially when administered to newborns and infants to prevent diseases of early childhood. Many means of attenuation have been shown to render vaccine strains susceptible to host defenses or unable to colonize lymphoid tissue effectively, thus decreasing their immunogenicity. We have constructed recombinant attenuated Salmonella vaccine strains that display high levels of attenuation while retaining the ability to induce high levels of immunogenicity and are well tolerated in high doses when administered to infant mice as young as 24 h old. The strains contain three means of regulated delayed attenuation, as well as a constellation of additional mutations that aid in enhancing safety, regulate antigen expression, and reduce disease symptoms commonly associated with Salmonella infec-tion. The vaccine strains are well tolerated when orally administered to infant mice 24 h old at doses as high as 3.5 108 CFU. Recombinant attenuated Salmonella vaccines (RASV) must decrease disease symptoms associated with infection but must also elicit a robust and lasting immune response to the vaccine. Unfortunately, many of the disease symptoms are caused by the same pathogenic strategies of Salmonella that are als