Activities of muscadine grape skin and polyphenolic constituents against H elicobacter pylori

Aims To identify active phenolic constituents in muscadine grape skin ( MGS ) extracts and determine interactions among compounds while further exploring their anti‐ H elicobacter pylori potential in vitro . Methods and Results The inhibitory effects of quercetin and resveratrol, active polyphenols identified in MGS extracts, against H . pylori were investigated. Quercetin and resveratrol significantly ( P  <   0·05) reduced H . pylori counts regardless of p H with minimal bactericidal concentrations of 256 and 128 μg ml −1 , respectively. MGS extracts displayed the highest efficacy, suggesting additional unidentified compounds not determined in this study. Time‐course viability experiments showed a dose‐dependent anti‐ H . pylori response to quercetin and resveratrol. Interestingly, neither quercetin nor resveratrol affected H . pylori outer membrane ( OM ) integrity as determined by 1‐ N ‐ phenylnaphthylamine ( NPN ) uptake assays. However, treatment with MGS extract did increase NPN uptake, indicating OM destabilization possibly by additional unknown components. Furthermore, quercetin was found to enter H . pylori as measured by HPLC supporting intracellular drug accumulation. Conclusions Quercetin and resveratrol possess strong anti‐ H . pylori activity in vitro and are independent of p H . Our results also suggest that these compounds do not affect H . pylori OM integrity as previously hypothesized and that the primary antimicrobial activity of quercetin may be linked to interactions with intracellular components. Significance and Impact of the Study The anti‐ H . pylori effects of quercetin and resveratrol suggest that these compounds may be useful in the dietary prevention and/or treatment of H . pylori infection.