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Infect. Immun. doi:10.1128/IAI.01908-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Immunization of pigs to prevent human disease: Construction and protective efficacy of a Salmonella Typhimurium live negative marker vaccine

Institute for Microbiology, Department of Infectious Diseases, University of Veterinary Medicine Hannover, Foundation, Hannover, Germany; Impfstoffwerk Dessau-Tornau GmbH, PSF 214, Rodleben OT Tornau, Germany; Department of Chemical Biology, Helmholtz Centre for Infection Research (HZI), Mascheroder Weg 1, D-38124 Braunschweig, Germany

^* To whom correspondence should be addressed. Email: gfgerlach{at}gmx.de.

	Abstract

Zoonotic infections caused by Salmonella Typhimurium pose a constant threat to consumer health with the pig being a major source particularly of multi-drug-resistant isolates. Vaccination, as a promising approach to reduce colonization and shedding, has been scarcely used as it interferes with current control programs relying on serology as a means for herd classification. In order to overcome this problem we set out to develop a negative marker vaccine allowing the differentiation of infected from vaccinated animals (DIVA concept). Applying an immunoproteomic approach with two dimensional gel electrophoresis, Western blot and quadrupole time of flight tandem mass spectrometry we identified the OmpD protein as a suitable negative marker. Using allelic exchange we generated an isogenic mutant of the licensed live vaccine strain Salmoporc® and showed that virulence of Salmoporc® and the mutant strain Salmoporc®ompD was indistinguishable in Balb/c mice. In a pig infection experiment including two oral immunizations with Salmoporc®ompD and challenge with a multiresistant S. Typhimurium DT104 clinical isolate, we confirmed the protective efficacy of Salmoporc®ompD in pigs showing a significant reduction of both clinical symptoms and colonization of lymph nodes and intestinal tract. OmpD immunogenic epitopes were determined by peptide spot array analyses. Upon testing of several 9-mer peptides, each including an immunogenic epitope, one peptide (position F₁₀₀-Y₁₀₈) was identified which facilitated the detection of infected animals independent of their vaccination status (DIVA function). The approach described overcomes the problems currently limiting the use of bacterial live vaccines and holds considerable potential for future developments in the field.