Lipopolysaccharide and lipopolysaccharide modification gene deletions affect TLR-4 mediated inflammatory signals in chicken oviduct cells and are potential safe live vaccines in production animals

Salmonella Enteritidis is the world's most common cause of salmonellosis in part because it has the ability to colonize the oviduct and contaminate eggs, while Salmonella Typhimurium is mainly a contaminant of pork and poultry meat. One of the important aspects of vaccine development is differentiation of infected from vaccinated animals. This can be achieved either by differentiation with regard to the serological response (DIVA concept) or else by the phenotype of the strain on bacteriological media. LPS mutants have been described as potentially being of value as live oral vaccine strains for both poultry and pigs, because they can be attenuated and have defects in TLR-4 signaling and thus induction of inflammation. For chickens, using the in vivo expression technology, it was shown that the rfbH gene, involved in lipopolysaccharide O-antigen synthesis, is transcriptionally induced during growth in whole eggs at room temperature. A S. Enteritidis ΔrfbH strain was unable to multiply in eggs at room temperature and did not survive in egg white at 42 degrees C. The attenuation was most likely caused by an increased susceptibility of the ΔrfbH mutant to yet undefined antibacterial components of the egg albumen. Knockouts of specific LPS modification genes, that alter the LPS structure by adding small molecules to the lipid A and LPS core structure, had an egg white survival defect and showed not to activate TLR-4 mediated downstream mediators (IL-1, IL-6, TNF-alpha). These gene deletions can thus be added to the list of potential targets when producing live attenuated vaccines. Gene deletions would also alter serologic responses against the LPS so that vaccinated birds can be differentiated from challenged birds. This was shown for piglets, in which immunization with ΔrfaJ and ΔrfaL mutants resulted in the induction of a serological response lacking detectable antibodies against LPS. The strains protected mice against Salmonella Typhimurium infection when orally administered.
 
Keywords: Salmonella, LPS, vaccines.

Abstract presented at the 3rd International Symposium on Alternatives to Antibiotics 2019.