Salmonella Typhimurium lacking the Znuabc transporter is attenuated and immunogenic in pigs

Abstract

Meat contamination by Salmonella spp is emerging as a major cause of human enteric infections in industrialized countries. The attempts to reduce human cases of salmonellosis encompass pre- and post harvest interventions. In this context, vaccination of pigs may represent an effective instrument in eliminating/reducing Salmonella burden through the food chain. We have previously demonstrated that Salmonella Typhimurium lacking the ZnuABC transporter (S. Typhimurium ΔznuABC) is a promising candidate live vaccine in different mouse models of Salmonella Typhimurium infection. In this study, we confirmed in pigs the attenuation of S. Typhimurium ΔznuABC. Moreover, we evaluated the safety and immunogenicity of S. Typhimurium ΔznuABC administered to pigs by the oral route. We monitored clinical conditions of animals and we conducted a microbiological culture and a quantification of the humoral and cellular immune response, respectively, on faecal and blood samples of pigs. After vaccination with attenuated S. Typhimurium ΔznuABC, pigs showed a modest degree of hyperthermia. In addition, faecal shedding of S. Typhimurium ΔznuABC could not be detected 28 days after the inoculum. Furthermore, vaccination with S. Typhimurium ΔznuABC elicited a distinct production of anti-Salmonella antibodies and IFN-γ. Taken together, these results suggest that S. Typhimurium ΔznuABC is attenuated and immunogenic in pigs. Although the vaccine dosages do not guarantee complete safety there is ample margin to set up better conditions of use, suggesting that S. Typhimurium ΔznuABC could be a promising attenuated strain to be used as live mucosal vaccine for oral delivery.

Parenteral administration of attenuated Salmonella Typhimurium ΔznuABC is protective against salmonellosis in piglets

“…In previous studies, we showed that S. Typhimurium lacking the ZnuABC transporter is an effective oral vaccine in preventing disease and in reducing colonization of gut and systemic organs of pigs experimentally challenged with virulent Salmonella microorganisms [19,20]. The results presented herein, corroborate and extend these findings, and also show that pigs intramuscularly vaccinated with S. Typhimurium znuABC exhibit a degree of protection against virulent S. Typhimurium infection comparable to that observed in orally vaccinated animals.…”

“…Typhimurium ATCC14028 and its isogenic mutant strain denominated S. Typhimurium znuABC were used in this study. Attenuated strain (S. Typhimurium znuABC) was produced according to the method previously described [17][18][19]. Wild type and mutant strains were cultured at 37 • C in Brain Heart Infusion (Oxoid Ltd., Basingstoke, UK), harvested by centrifugation and then washed twice in ice-cold Phosphate Buffer Solution (PBS) (Sigma-Aldrich, Milan, Italy).…”

“…Suspect Salmonella colonies underwent biochemical identification by BBL Enterotube II (BD Franklin Lakes, NJ, USA) and serological identification using Salmonella group specific antisera. This semi-quantitative approach enabled the determination of the likely concentration of Salmonella in each sample [17][18][19].…”

“…This Salmonella strain is attenuated due to its inability to efficiently recruit zinc in the infected host and it is protective in both mouse and pig models of salmonellosis [1,[17][18][19][20].…”

“…In addition, we used a new challenge model in order to simulate a natural infection, when vaccinated and naïve piglets were co-housed with piglets that were shedding wild type S. Typhimurium. More specifically, this challenge model was different from the challenge model used in our previous study in which vaccine and virulent strain of S. Typhimurium were intragastrically administered to pigs [19,20].…”