Screening And Identification Of Bacteria Metabolizing Quercetin, Determination And Biological Activity Of Metabolites

Quercetin has a wide range of possible biological properties. In the process of humandaily feeding, part of quercetin is coerced to colon after ingested and can exert effects on gutmicrobiota; and the gut microflora also can alter its biological activity and their potentialfunctional effects. The interaction between quercetin and gut microbiota will influence bodyhealth.There still is a lack of information about gut bacteria involved in this process and thefunction of quercetin metabolites.In this study, the strains of gut microbes from human feces that can transform quercetinwere separated and identified by in vitro fermentation, their potention catabolites wereanalyzed with HPLC and MS, and the biological activity of the mixture solution of catabolites(MSCs) such as the antioxidant activites, cytotoxic activities and the inhibition of fivepathogenic bacteria species were determined in vitro. The results showed that:（1）Escherichia coli, Streptococcus lutetiensis, Lactobacillus acidophilus, Weissellaconfusa, Enterococcus gilvus, Clostridium perfringens and Bacteroides fragilis were isolatedand identified, and their degrading ability were different. Among them, C. perfringens and B.fragilis were discovered to have the strongest ability of degrading quercetin, the other strainscould only partly degrading quercetin. Additionally, quercetin couldn’t inhibit the growth of C.perfringens.（2）One metabolite,3,4-Dihydroxyphenylacetic acid that was produced by both C.perfringens and B. fragilis transforming quercetin. No other metabolites were detected in theother fermented broths. The antioxidant activities of all strains fermenting quercetin reachedthe highest values at the concentration of1mg/mL quercetin in broth; and the fermentedproducts of C. perfringens and B. fragilis presented stronger activities than that of other strainsat most concentrations of quercetin in broth. Additionaly, all of the fermented broths presenteda decline of the antioxidant activities compared to quercetin.（3）The metabolites from C. perfringens and B. fragilis exerted a strong inhibitory effect(P<0.05) on HCT-116cells, but W. confusa acted stronger (P<0.01) on both A549cells andHeLa cells than the others, and C. perfringens acted the second stronger inhibition effect on HeLa cells than others. Other metabolites have a similar or decreased inhibitory ability onhuman cancer cells compared to quercetin itself. This inhibitory effect had not been detected ofquercetin and the MSCs on five common pathogenic bacteria species. However, this studyreported that some gut bacteria could improve the function of quercetin inhibiting cancer cellsafter quercetin was fermented by them.In conclusion, this experiment isolated seven fecal bacterial strains with ability oftransforming quercetin, and discovered these bacteria can change the biological activity ofquercetin. Specially, several strains can improve the function of quercetin inhibiting cancercells. This work helps understand the the interaction of quercetin and gut microbiota, andprovides a reference to discover the more possibility of phytochemicals on human helth.