Butyrate-mediated autophagy inhibition limits cytosolic Salmonella Infantis replication in the colon of pigs treated with a mixture of Lactobacillus and Bacillus

Probiotics as an effective and safe strategy for controlling Salmonella infection are much sought after, while autophagy is a central issue in eliminating intracellular pathogens of intestinal epithelial cells. In this study, an animal model of colitis has been developed by infecting weaned pigs orally with a strain of Salmonella Infantis in order to illuminate the potential efficacy of a mixture of Lactobacillus and Bacillus (CBB-MIX) in the resistance to Salmonella infection by regulating butyrate-mediated autophagy. We found that CBB-MIX alleviated S . Infantis-induced colitis and tissue damage. Autophagy markers ATG5, Beclin-1, and the LC3-II/I ratio were significantly enhanced by S . Infantis infection, while treatment with CBB-MIX suppressed S . Infantis-induced autophagy. Additionally, S . Infantis-induced colonic microbial dysbiosis was restored by this treatment, which also preserved the abundance of the butyrate-producing bacteria and the butyrate concentration in the colon. A Caco-2 cell model of S . Infantis infection showed that butyrate had the same effect as the CBB-MIX in restraining S . Infantis-induced autophagy activation. Further, the intracellular S . Infantis load assay indicated that butyrate restricted the replication of cytosolic S . Infantis rather than that in Salmonella -containing vacuoles. Suppression of autophagy by knockdown of ATG5 also attenuated S . Infantis-induced cell injury. Moreover, hyper-replication of cytosolic S . Infantis in Caco-2 cells was significantly decreased when autophagy was inhibited. Our data demonstrated that Salmonella may benefit from autophagy for cytosolic replication and butyrate-mediated autophagy inhibition reduced the intracellular Salmonella load in pigs treated with a probiotic mixture of Lactobacillus and Bacillus.