S. Typhimurium and S. Typhimurium Monophasic variant attenuated vaccines. A comparison of efficacy in homologous and heterologous infection in piglets

Introduction: Salmonella Typhimurium and its monophasic variant (S. Typhimurium 1, 4, [5], 12:i-) are increasingly responsible of food borne infections in humans and pork represents the principal source of infection. Infection is generally sub-clinical in pigs and carrier pigs could introduce bacteria in the slaughterhouse. The aim of the study was to test the efficacy and safety of an attenuated vaccine of S. Typhimurium 1, 4, [5], 12:i- (S. Typhimurium Monophasic variant ΔznuABC) during an homologous and heterologous infection, with a field isolated strain of S. Typhimurium. The efficacy and safety of S. Typhimurium Monophasic variant ΔznuABC was compared to an attenuated strain of S. Typhimurium (S. Typhimurium ΔznuABC). Materials and Methods: Twenty eight weaned piglets were divided in 3 groups and acclimatized for a week. Group T was composed of 8 piglets vaccinated with an oral administration of S. Typhimurium ΔznuABC at the final dose of 5 х 107 CFU. Group M was composed of 10 piglets vaccinated with an oral administration of S. Typhimurium Monophasic variant ΔznuABC at the final dose of 5 х 107 CFU. Group C was composed of 10 unvaccinated piglets. At day 35 after vaccination, all piglets were challenged by an oral gavage with 5 х 108 CFU of S. Typhimurium Monophasic variant or S. Typhimurium. Particularly, piglets from group T were divided in 2 groups: 3 piglets were infected with S. Typhimurium, the other 5 piglets were infected with S. Typhimurium 1, 4, [5], 12:i-. Piglets from group M were divided in 2 groups: 5 piglets were infected with S. Typhimurium. The other 5 piglets were infected with S. Typhimurium 1, 4, [5], 12:i-. Unvaccinated piglets were divided in 2 groups: 5 piglets were infected with S. Typhimurium, the other 5 piglets were infected with S. Typhimurium 1, 4, [5], 12:i-. Analyzed parameters were weight, temperature, fecal shedding and organ colonization. Results: In control groups, the amount of S. Typhimurium in feces tends to be higher than S. Typhimurium 1, 4, [5], 12:i- from challenge to the end of the trial and temperature was significantly different at day 1 after infection indicating that S. Typhimurium was more virulent than S. Typhimurium 1, 4, [5], 12:i-. The safety of vaccine strains was monitored analyzing fecal shedding and growth of animals. Conclusion: Attenuated vaccines were safe, in fact they were not isolated in feces after three weeks from vaccination and did not affected growth of animals. Furthermore, both attenuated vaccines reduced the shedding of virulent strains in comparison to unvaccinated groups and S. Typhimurium ΔznuABC appeared more effective in homologous and heterologous challenge infections.