Inhibitory Effect And Mechanism Of Syringaldehyde Against Salmonella Type ? Secretion System

Salmonella enterica,one of the zoonotic pathogens of great significance in global public health.It could cause a vierty of serious diseases and also lead significant economic losses to the livestock and poultry industry.At present,the traditional method for treating Salmonella infection is to use antibiotics.However,with the continuous emergence and widespread existence of Salmonella drug resistance,treatment with salmonellosis has escalated.Therefore,it is urgent to seek new drugs or replacement strategies to combat Salmonella infection.Compared with traditional antibiotics,it is an ideal strategy for drug development by inhibiting key virulence factors of bacterial rather than killing them directly.Salmonella enhances pathogenicity through SPI-mediated T3 SS during infection.In fact,the deletion of effector proteins or genes of T3 SS will not affect the growth of Salmonella,but its infection ability is reduced or even lost.Therefore,T3 SS has become an ideal target for anti-infective drug screening.Herbal medicine has a long application history in China.It has many advantages such as wide distribution,diverse biological activities,low cost,few side effects,and difficulty in inducing drug resistance.Therefore,Salmonella T3 SS has become an ideal target for drug screening,and the research of antiviral drugs in traditional Chinese medicine has become our research target.In this study,a T3 SS SipB-?-lactamase fusion protein reporter system was constructed,and the effector protein transport function of T3 SS was used as an inhibitor screening target derived from natural compounds.Through the screening,it was found that syringaldehyde,myricetin,and paeonol can significantly inhibit the T3 SS effector protein transport without antibacterial activity.In vitro drug activity evaluation,syringaldehyde can significantly reduce the adhension to host cells and the cell damage.In order to clarify the mechanism of inhibition of Salmonella T3 SS function,through biochemical,molecular biology,and high-throughput sequencing transcriptomics analysis,it was found that syringaldehyde showe significant expression levels of effector proteins and regulatory protein of T3 SS.High-throughput sequencing transcriptomics analysis found that the mRNA transcription levels of multiple differentially expressed genes in Salmonella were significantly down-regulated after treatment with syringaldehyde,it was found that syringaldehyde targets the hilD-hilC-rstA-hilA regulatory pathway in T3 SS and inhibited the expression of downstream effector proteins and regulatory protein.Experimental therapeutics of a mouse model of Salmonella infection shows that syringaldehyde treatment prolong the survival time and improve the survival rate of Salmonella-infected mice;histopathological analysis found that syringaldehyde relieve Salmonella typhi pathological damage to the liver,spleen,and cecum of mice;The determination of cecum cytokines found that syringaldehyde treatment significantly reduced cytokines(IL-1?,IL-6,TNF-? in cecum tissue of infected mice)and IFN-?)content.In summary,this study was conducted the inhibitor screening,in vitro and in vivo activities and mechanism of action,and found that syringaldehyde can inhibit the invasion into host cells and bacterial-mediated damage;Syringaldehyde inhibits the pathogenicity of Salmonella by inhibiting the hilD-hilC-rstA-hilA regulatory network pathway of T3 SS,reducing the expression of effectors(SipA,SipB and SipC)and regulatory proteins(HilA)and has a systemic protective effect on Salmonella infected mice.This study provides the basis and strategy for the development of anti-infective drugs targeting bacterial T3 SS,and also provides candidate compounds for anti-Salmonella infection.