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Salmonella en filière porcine : dynamique d’infection, pouvoir colonisateur et virulence

Abstract : Salmonella is the second leading cause of human zoonoses in the European Union and represents a major challenge for the pork industry. Serovars S. Typhimurium, S. Derby and the monophasic variant of S. Typhimurium, implicated in human salmonellosis, are highly prevalent in pigs and also in human. The objectives of this research were to establish the infection dynamics in pigs by Salmonella under conventional and experimental rearing conditions, to evaluate pig colonization ability and pathogenicity in humans of the three serovars. In conventional farms, the serological monitoring of Salmonella antibodies allowed to evaluate the average age of seroconversion at 137 days and to identify a "farm effect" on the age of seroconversion. The first trial under experimental conditions revealed that pigs inoculated with the monophasic variant of S. Typhimurium excreted this serovar continuously in the feces. At autopsy dates 21, 49 or 84 days after inoculation, Salmonella were found in the different parts of the intestine, in the lymph nodes and at very high levels in the tonsils. After passage through the digestive tract, different MLVA profiles from that of the inoculated strain were identified suggesting that the genome of the strain has evolved. The second attempt to compare the colonizing ability in the pigs of the three serovars showed that the dynamics of excretion and colonization were similar regardless of the serovar. However, the amount excreted was significantly different: higher with the monophasic variant compared to S. Typhimurium. The pathogenicity in humans of 15 strains of porcine origin belonging to the 3 serovars was evaluated in vivo on an insect model Galleria mellonella, and in vitro on Caco-2 cells. The strains were found to be potentially virulent. On Caco-2, the monophasic variant had the highest cell adhesion percentage and Derby, the lowest. Different levels of virulence were observed between strains of the same serovar. This work brought new knowledge on the Salmonella issue in the pig sector.
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María Belén Cevallos Almeida. Salmonella en filière porcine : dynamique d’infection, pouvoir colonisateur et virulence. Sciences agricoles. Université Rennes 1, 2018. Français. ⟨NNT : 2018REN1B013⟩. ⟨tel-01895442⟩

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