||Salmonella infection in humans is commonly manifested as enterocolitis characterized by induction of epithelial secretion of pro-inflammatory cytokines and diarrhea, accompanied by infiltration of neutrophils in the intestinal submucosa, which is a hall-mark of intestinal inflammation. The recruitment of neutrophils from circulation to the subepithelial region is facilitated by chemokines such as interleukin-8 (IL-8), which is known to be significantly induced upon bacterial entry by host epithelial cells.|
Probiotics are able to be used in the prevention or treatment of certain types of in-flammatory bowel disease (IBD). Certain types of Lactobacillus strains are successful in modulating pro-inflammatory cytokine signaling, which in turn, reduce inflammation in the gastrointestinal tract.
In this study, we used the human intestinal cell line HCT 116 as an intestinal epithelial model, and the human leukemic monocyte cell line THP-1 as a leukocyte model, to determine the effects of four arbitrarily chosen strains of Lactobacillus probiotics on inflammation caused by Salmonella infection. The Salmonella strain used in the study is the wild-type SL1344, grown under anaerobic conditions to late log phase to maximize invasion phenotype. The four probiotic strains are Lactobacillus acidophilus, Lactoba-cillus rhamnosus, Lactobacillus paracasei, and Lactobacillus delbrueckii.
Our results show that all four strains of probiotics were able to sporadically reduce mRNA expression of the three tested cytokines, but only Lactobacillus paracasei was able to consistently lower IL-8 expression. Our experimental results had shown in infection tests that upon Salmonella infection, the most acute response is seen in the upregu-lation of IL-8 expression, suggesting a possible relation between inflammation induced by bacterial infection and IL-8 induction. However, invasion assays show that Lactoba-cillus paracasei did not significantly reduce the amount of intracellular bacteria. In-stead, only Lactobacillus rhamnosus, which did not consistently suppress IL-8, signifi-cantly reduced bacterial invasion. These findings suggest that various probiotics sup-press inflammation through different mechanisms, and that the probiotic Lactobacillus rhamnosus is able to protect intestinal epithelial cells by rendering them less suscepti-ble to Salmonella invasion.