摘要Gut bacterial nitroreductases play an important role in reduction of various nitroaromatic compounds to the corres-ponding N-nitroso compounds,hydroxylamines or aromatic amines,most of which are carcinogenic and mutagenic agents.Inhibition of gut nitroreductases has been recognized as an attractive approach for reducing mutagen metabolites in the colon,so as to prevent colon diseases.In this study,the inhibitory effects of 55 herbal medicines against Escherichia coli(E.coli)nitroreductase(EcNfsA)were examined.Compared with other herbal extracts,Syzygium aromaticum extract showed superior inhibitory potency toward EcNf-sA mediated nitrofurazone reduction.Then,the inhibitory effects of 22 major constituents in Syzygium aromaticum against EcNfsA were evaluted.Compared with other tested natural compounds,ellagic acid,corilagin,betulinic acid,oleanic acid,ursolic acid,urolith-in M5 and isorhamnetin were found with strong to moderate inhibitory effect against EcNfsA,with IC50 values ranging from 0.67 to 28.98 mol·L-1.Furthermore,the inhibition kinetic analysis and docking simulation demonstrated that ellagic acid and betulinic acid po-tently inhibited EcNfsA(Ki＜2 μmol·L-1)in a competitively inhibitory manner,which created strong interactions with the catalytic tri-ad of EcNfsA.In summary,our findings provide new scientific basis for explaining the anti-mutagenic activity of Syzygium aromatic-um,where some newly identified EcNfsA inhibitors can be used for developing novel agents to reduce the toxicity induced by bacteri-al nitroreductase.