Investigation of dietary rice bran for protection against Salmonella enterica Typhimurium infection in mice
Date
2014
Authors
Kumar, Ajay, author
Ryan, Elizabeth P., advisor
Dow, Steven, committee member
Leach, Jan, committee member
Schenkel, Alan, committee member
Weir, Tiffany, committee member
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Abstract
Rice bran is a byproduct of rice milling for white rice. Rice bran is a rich source of nutrients such as vitamins, minerals, soluble and insoluble fibers, fatty acids, polyphenols and proteins. Research has shown the beneficial health effects of rice bran in hyperlipidemia, diabetes, immune modulation, allergies and cancer. This dissertation focuses on evaluation of rice bran for protection against Salmonella using a mouse model of oral infection. Salmonella is a food and water borne pathogen that affects a variety of hosts including plants, animals and humans. Salmonella infections are a major public health challenge around the globe. Currently, salmonellosis is treated using high doses of synthetic antimicrobials and the problem of drug resistance has increased. In this scenario, alternative and sustainable interventions are needed to control Salmonella infections. Several dietary agents have been studied for protective effects in Salmonella infection models. We tested the prophylactic effects of dietary rice bran in a Salmonella model of infection using female 129S6/SvEvTac mouse model with infection of Salmonella enterica Typhimurium 14028s strain. Feeding of 10% dietary rice bran for one week prior to infection significantly (p<0.05) reduced fecal excretion of Salmonella in orally infected mice. Salmonella-infected, rice bran fed mice also showed a significant decrease in systemic inflammatory cytokines such as TNF-α, IFN-γ and IL-12 as compared to control diet fed animals. The colonization resistance against enteric pathogens is highly influenced by composition of gut microflora. Supplementation of dietary rice bran increased the number of Lactobacillus spp. in feces of mice as compared to mice that were fed control diet. Research has shown that oral administration of some species of Lactobacillus reduces the colonization of Salmonella. We hypothesized that rice bran components also enhance mucosal protection by preventing Salmonella entry into the epithelial cells. Methanolic rice bran extracts were assessed in mouse small intestinal epithelial (MSIE) cells for blocking Salmonella entry and intracellular replication. Rice bran extract significantly reduced Salmonella entry and intracellular replication into MSIE cells. These results suggest the potential mechanisms for dietary rice bran induced improvement of colonization resistance against Salmonella. Given that rice crops have a large variation in genotype and phenotype such as in yield, disease and pest resistance, drought resistance, and nutrient quality, we hypothesized that variation in rice bran across cultivars induces differential protection against Salmonella infection due to differences in their phytochemical profile. A panel of six varieties namely IAC 600, Jasmine 85, IL 121-1-1, Wells, Red Wells and SHU 121 were tested in the in vitro and in vivo model of Salmonella infection. We found that rice bran extracts across varieties inhibited Salmonella entry into the MSIE and Caco-2 cells to different extents. IAC 600 fed animals significantly (p<0.05) reduced Salmonella fecal excretion as compared to the control diet fed animals. IAC 600 fed animals also reduced Salmonella fecal shedding significantly (p<0.05) as compared to SHU 121 diet fed animals at 2 and 6 days post Salmonella infection. Histopathological analysis revealed that IAC 600 diet fed animals had better ileal pathological scores as compared to SHU 121 and the control diet fed animals post Salmonella infection. SHU 121 and the control diet fed groups showed higher ulceration and inflammatory changes in ileum as compared to IAC 600 fed animals. Next we analyzed the fatty acid profile, mineral profile and total phenolic contents of rice bran. Stearic acid, lignoceric acid, boron and total phenol content were significantly correlated with Salmonella fecal shedding in mice across varieties. However, further studies are required to confirm the role of these nutrients from rice bran in protection against Salmonella. These results suggest that the variety of rice plays an important role in bran-induced protection against Salmonella infection and this difference in protection across the varieties could be attributed to a combination of bioactive components. Our studies suggest that dietary rice bran improves colonization resistance against Salmonella in mice. Rice bran could have important role in prevention of enteric infections in resource scarce populations and further human clinical studies are required. Rice bran may also be evaluated for supplementing diets of food animals to prevent Salmonella infections and therefore could have a potential role in food safety.
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Subject
rice variety
Salmonella
rice bran
fecal shedding
inflammation