Cell Surface Display of Salmonella Outer Membrane Protein A on Lactobacillus salivarius: A First Step Towards Food-Grade Live Vaccine Against Salmonella Infections

Abstract

As one of the most important pathogens in both humans and animals, Salmonella is a significant health problem, especially in the developing countries. Outer membrane protein A (OmpA) is among the major outer membrane proteins of Salmonella with strong immunogenicity. Vaccination is an effective tool for the prevention of Salmonella infections. Lactic acid bacteria are the normal flora of gastrointestinal (GI) tract. In this research, lactobacilli from different parts of chicken GI tract were isolated and evaluated for bile salts and acidic pH tolerance. One strain isolated from the small intestine was identified as Lactobacillus salivarius by carbohydrate fermentation test and 16SrRNA partial sequencing. To address the need for safe oral vaccine to control Salmonella infection, we engineered this natural chicken isolate of L. salivarius to express OmpA under promotion of Lactate dehydrogenase (ldh) promoter. The surface displayed OmpA reacted with anti-OmpA in ELISA, Immunoblotting and flow cytometry assays, suggesting that the expressed protein adopted a native conformation. Strong agglutination reaction of the recombinant lactobacilli with sera of the naturally Salmonella infected chickens showed the multivalency and overexpression of the OmpA on the surface of L. salivarius. Experimental infection assay confirmed that the engineered commensal bacteria could be an attractive candidate as food-grade live vaccine against Salmonella infections.

Keywords:

• recombinant OmpA
• Salmonella
• lactic acid bacteria
• ldh promoter

ACKNOWLEDGMENTS

We thank Professor M. Zahraei, Veterinary Faculty, Tehran University of Medical Sciences, Iran, for kindly providing Salmonella strains and Professor J. Kok, Department of Genetics, University of Groningen, Netherlands, for kindly providing Plasmid pMG36e.