Inhibitory Effect Of Sulfur-containing Flavors On Gram-positive Pathogenic Bacteria And Regulation Of Virulence Genes

In the food spices,sulfur-containing flavors occupy a very important position.Sulfur-containing flavors are characterized by low aroma threshold,small dosage,strong characteristic,usually as an infinitesimal fragrant ingredient of food.The important chemical composition of cruciferous vegetables is isothiocyanates sulfur-containing compound,with anti-inflammatory,antibacterial and antioxidant effect.Sulfide flavors are the largest group of edible sulfur-containing compounds.In this paper,nine kinds of isothiocyanate flavors and ten kinds of sulfide flavors were selected,and the antibacterial activities of sulfur-containing flavors against Staphylococcus aureus and Listeria monocytogenes were determined by measuring the diameter of inhibition zone.The effect of structure on their antibacterial activities was further investigated,the minimum inhibitory concentration(MIC)of sulfur-containing flavors was determined using a broth microdilution method,and growth curve based on OD600m valued,laid the foundation for revealing the mechanism of antimicrobial activity of sulfur-containing compounds and the structure-activity relationship.The results showed that Benzyl isothiocyanate(BZITC),Phenethyl isothiocyanate(PEITC)and 3-Methylthiopropyl isothiocyanate(MTPITC)had better inhibitory effect against two gram-positive bacteria,and the inhibitory effects were followed the order of BZITC ≈ PEITC>MTPITC at concentration of 0.08 mol/L.These results suggest that the benzene ring plays an important role in the antibacterial activity of isothiocyanate flavors against gram-positive pathogens.For sulfide flavors at a concentration of 5 mol/L,the diallyl disulfide(DADS),methyl furfuryl disulfide(MFDS)and furfuryl isopropyl sulfide(FIPS)had significant inhibitory effect against two gram-positive bacteria.DADS showed the highest inhibitory effect.These results show that the presence of double bond or allyl group may enhance the antibacterial activity of sulfide flavors.BZITC and DADS showed the highest inhibitory effect against S.aureus,the minimal inhibitory concentration were 0.61 mmol/L and 310.25 mmol/L.Staphylococcus aureus can produce a variety of virulence-related toxins and extracellular enzymes,the thermostable nuclease encoded by the nuc gene is a characteristic marker for detection of food contamination and infection caused by S.aureus.In this paper,by adding sub-inhibitory concentration of BZITC and DADS,the thermostable nuclease(nuc)gene of S.aureus expression was studied by real-time reverse transcriptase PCR.The result showed that treatment of BZITC at sub-inhibitory concentrations raging from 1/4MIC、1/8MIC、1/16MIC、1/32MIC to 1/64MIC,by comparing control group,relative expression of the nuc in S.aureus were decreased to 13.42%、29.00%.47.05%、52.19%and 68.87%respectively.Sub-inhibitory concentrations of DADS also inhibited the expression of the nuc obviously,and a dose-dependent attenuation of nuc production was observed in S.aureus.Therefore,BZITC and DADS may be useful in the attenuation of nuc producing S.aureus food poisoning and infections.