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Vaccination of laying hens has been successfully used to reduce egg contamination by  Salmonella  Enteritidis, decreasing human salmonellosis cases worldwide. Currently used vaccines for layers are either inactivated vaccines or live attenuated strains produced by mutagenesis. Targeted gene deletion mutants hold promise for future vaccines, because specific bacterial functions can be removed that may improve safety and allow differentiation from field strains. In this study, the efficacy of  Salmonella  Enteritidis  ΔtolC  and  ΔacrABacrEFmdtABC  strains in laying hens as live vaccines was evaluated. The mutants are deficient in either the membrane channel TolC ( ΔtolC ) or the multi-drug efflux systems acrAB, acrEF and mdtABC ( ΔacrABacrEFmdtABC ). These strains have a decreased ability for gut and tissue colonization and are unable to survive in egg white, the latter preventing transmission of the vaccine strains to humans. Two groups of 30 laying hens were orally inoculated at day 1, 6 weeks and 16 weeks of age with 10 8  cfu of either vaccine strain, while a third group was left unvaccinated. At 24 weeks of age, the birds were intravenously challenged with 5 × 10 7  cfu  Salmonella  Enteritidis PT4 S1400/94. The vaccine strains were not shed or detected in the gut, internal organs or eggs, 2 weeks after the third vaccination. The strains significantly protected against gut and internal organ colonization, and completely prevented egg contamination by  Salmonella  Enteritidis under the conditions of this study. This indicates that  Salmonella  Enteritidis  ΔtolC  and  ΔacrABacrEFmdtABC  strains might be valuable strains for vaccination of layers against  Salmonella  Enteritidis.

veterinary research

Prevention of egg contamination by Salmonella Enteritidis after oral vaccination of laying hens with Salmonella Enteritidis ΔtolC and ΔacrABacrEFmdtABC mutants