Protective action of S-layer proteins from Lactobacillus paracasei M7 against Salmonella infection and mediated inhibition of Salmonella-induced apoptosis

摘要

Surface layer proteins had been proposed that it could protect human intestine from pathogens and aid in maintaining cellular integrity. However, the functions of S-layer proteins have not yet been fully revealed, and it has been proposed that these structures protected the intestinal microbes from hostile environmental agents. In this study, the ability of the Lactobacilli to inhibit adhesion of Salmonella to intestinal mucosa was studied on cultured HT-29 cells. Lactobacillus paracasei M7 was shown to inhibit the adhesion of Salmonella to epithelial cells, a process which may be related to the specific component of the bacterial surface. Human epithelial HT-29 cells were treated with S-layer proteins after Salmonella injection and pretreated with S-layer proteins to determine their importance in the inhibition of pathogen adherence. According to the analysis of cell cycle by flow cytometry, the HT-29 cells treated by Salmonella in S phase were 26.88 % compared with 36.70 % in the normal HT-29 cells. However, the addition of S-layer proteins made the HT-29 cells in S phase increase to 30.13 %. The activity of caspase-3 in the HT-29 cell was determined using a caspase-3 activity kit, which indicated the degree of apoptosis. Moreover, we also found that Lactobacillus S-layer proteins could protect Salmonella-induced apoptosis through reducing the caspase-3 activity. This mechanism might represent a novel approach for antagonizing Salmonella infection.