Investigating the effects of oryzatensin on gut microbiota growth using a novel quantitative standard curve-fitting method: an ex-vivo study

Objective: Oryzatensin (ORZ) is a refractory, bioactive peptide that is isolated from rice. In the current study, we investigated the effect of ORZ on the growth of gut microbiota. Methods: Ten apparently healthy subjects were enrolled in the current ex vivo study. Casual stool specimens were obtained from the subjects, then Enterobacteriaceae, Bacilaceae, and probiotic bacterial families were isolated using MAC, MYP, and MRS agars, respectively. The effect of exposure to different concentrations of ORZ (10-4, 10-5, 10-6, and 10-7 mol/L) on the growth of these bacteria was evaluated using the standard curve-fitting method, instead of standard qualitative methods such as MBC and MIC, because of the absence of detectable optical differences among the wells. The bacterial quantity was determined by evaluation of the suspensions turbidity at 492 to 630 nm. Results: ORZ had an antibacterial effect and negatively controlled the growth of all isolated species compared with the control group. The inhibitory effect of ORZ was most significant at the dose of 10-7 mol/L (not significant at 10-5 and 10-6 mol/L and significant at 10-4 mol/L) for bifidobacteria and 10-4 mol/L for Enterobacteriaceae, Bacilaceae, and lactic acid bacteria. Conclusion: The findings of the current study reveals that ORZ and possibly rice can reduce intestinal total bacterial count. Moreover, considering the carcinogenic effects of final metabolites of the enteral bacteria, such as free radicals, ORZ and rice may have an antineoplastic effect.