Effect Of Sulfur-containing Flavors On The Expression Of Virulence Genes In Salmonella Pathogenicity Island 1

In order to deal with the increment of multidrug-resistant Salmonella strains caused by antibiotics treatment and meet consumers’ pursuit of food safety and nutrition,relative research about natural antibacterial agents with antivirulence potency has attracted wide attention.Sulfur-containing flavors acted as one of natural flavor substances and a class of food additives,which not only play a key part in enriching food flavor,but also presented favorable effects in antibacterial activity.Salmonella enteric has a high infection rate in both human and animals,including many different kinds of serotypes which can cause gastroenteritis and even systemic infection.The pathogenic properties of S.enteric are relevant to the interactions between virulence factors distributed in pathogenicity islands,fimbriae,lipopolysaccharide and so on.Relying on our previous studies,three kinds of sulfur-containing flavors with obvious inhibitory effects on gram-negative bacteria were selected,and S.enteric strain ATCC14028 was used as the tested strain.A broth microdilution method was undertaken to determine the minimum inhibitory concentrations(MICs)of three selected sulfur-containing flavors against S.enteric,and spectrophotometry was conducted to investigate their influence on the growth of the strain.Furthermore,the effect of subinhibitory concentrations of sulfur-containing flavors on transcription of virulence genes(hilA,hilC and hilD)and the quorum sensing gene(sdiA)in S.enteric was investigated by real-time reverse transcriptase PCR.Additionally,the efficacy of sulfur-containing flavors on the biological characteristics of S.enteric,including swimming motility assay,measurement of intra-and extracellular ATP and scanning electron microscopy(SEM)observation were also determined.The MIC value of benzyl isothiocyanate(BITC)against S.enteric was 1 mmol/L,while diallyl disulfide(DADS)and methyl furfuryl disulfide(MFDS)were both 2 mmol/L.At subinhibitory concentrations,three kinds of sulfides reduced the expression levels of hilA,hilC and hilD in dose-dependent manners.Moreover,BITC and DADS can suppress the expression of sdiA gene.Motility assay showed that DADS and MFDS could decrease bacterial swimming motility significantly.The treatment with sulfur compounds affected theintegrity of cell wall and cell membrane,inducing a decrease of the intracellular ATP level while an increase of the extracellular ATP level.In summary,the expression levels of virulence genes and the quorum sensing gene were down-regulated after being treated with three sulfur-containing flavors respectively,indicating that BITC,DADS and MFDS may repress the formation of S.enteric virulence.Besides,changes in the biological properties indicate that sulfur-containing flavors have the potential to regulate the biological activities of S.enteric.Therefore,sulfide flavors represented by BITC,DADS and MFDS may display preventive effects on S.enteric,having the potential to control food-borne diseases caused by this bacterium.