Dietary rice bran promotes resistance to Salmonella enterica serovar Typhimurium colonization in mice

Abstract

Background: Dietary rice bran consists of many bioactive components with disease fighting properties; including the capacity to modulate the gut microbiota. Studies point to the important roles of the gut microbiota and the mucosal epithelium in the establishment of protection against enteric pathogens, such as Salmonella. The ability of rice bran to reduce the susceptibility of mice to a Salmonella infection has not been previously investigated. Therefore, we hypothesized that the incorporation of rice bran into the diet would inhibit the colonization of Salmonella in mice through the induction of protective mucosal responses.

Results: Mice were fed diets containing 0%, 10% and 20% rice bran for one week prior to being orally infected with Salmonella enterica serovar Typhimurium. We found that mice consuming the 10 and 20% rice bran diets exhibited a reduction in Salmonella fecal shedding for up to nine days post-infection as compared to control diet fed animals (p < 0.05). In addition, we observed decreased concentrations of the pro-inflammatory cytokines, TNF-alpha, IFN-gamma, and IL-12 (p < 0.05) as well as increased colonization of native Lactobacillus spp. in rice bran fed mice (p < 0.05). Furthermore, in vitro experiments revealed the ability of rice bran extracts to reduce Salmonella entry into mouse small intestinal epithelial cells.

Conclusions: Increasing rice bran consumption represents a novel dietary means for reducing susceptibility to enteric infection with Salmonella and potentially via induction of native Lactobacillus spp.

Figures

Figure 1

Effect of dietary rice bran onSalmonellafecal shedding of mice. Fecal shedding was examined in Salmonella infected animals fed control, 10% and 20% rice bran diet for 3 weeks (one week prior and 2 weeks post challenge). Data are shown as mean ± standard deviation of mean log10 CFU per gram of feces (n = 5 mice/diet group), and data are representative of three independently conducted experiments. Repeated measures ANOVA and post hoc Tukey’s test were applied. Significance is shown by * (P < 0.05) and ** (P < 0.01).

Figure 2

Effect of dietary rice bran on serum TNF- α, IFN-γ and IL-12 levels inSalmonellainfected mice. Blood was drawn at days 0, 7 and 14 following Salmonella infection and serum was analyzed for TNF- α (A), IFN-γ (B) and IL-12 (C) levels in control, 10% and 20% rice bran diet groups. Data are shown as mean ± standard deviation of mean (n = 3 mice/diet group). Significance was measured by two-way ANOVA and Bonferroni post hoc test.

Figure 3

Effect of dietary rice bran on fecalLactobacillusspp.Lactobacillus spp. DNA (pg/μl) from fecal pellets of mice before Salmonella infection (day 0) and at day 6 (post infection) was determined using qPCR. Error bars indicate standard deviation of mean and * (P < 0.05), ** (P < 0.01) and *** (P < 0.001) denote significant differences in rice bran fed mice from controls (n = 5 mice/diet group). Significance was tested by repeated measures ANOVA and Tukey’s post hoc test.

Figure 4

Effect of rice bran extract onSalmonellaentry and intracellular replication in MSIE cells. MSIE cells pre-incubated with rice bran extract (RBE) at doses of 0, 0.5, 1.0 and 2.0 mg/ml for 24 hours, followed by the co-incubation of the RBE with Salmonella showed significant inhibition of Salmonella entry (A). RBE was tested for effects on intracellular Salmonella replication inside MSIE cells for 24 hours (co-incubated with RBE) (B). Bacteria are shown as mean ± standard deviation of mean log10 CFU per mL of cell lysate (n = 3). Significance was determined using a nonparametric (Kruskal Wallis) ANOVA, followed by Dunn’s multiple means comparison. Statistical differences denoted by * (P < 0.05) and ** (P < 0.01).

Figure 5

Potential mechanisms involved in dietary rice bran induced reduction in susceptibility toSalmonellainfection. Rice bran may inhibit Salmonella colonization via modulation of gut microbiota, preventing cellular entry of Salmonella, and inhibiting intracellular replication.