Inhibitory Effect And Mechanism Of Tannic Acid Against Salmonella Type Three Secretion System

Salmonella is a zoonotic pathogen that causes gastroenteritis,typhoid fever,and septicemia in humans and animals.Salmonella are common and widely distributed across the globe,mainly colonizing the gastrointestinal tracts of mammals and reptiles.Currently,antibiotics are the most common treatment for Salmonella infection.Although positive therapeutic effects have been achieved with antibiotic therapy,this has also promoted the development of bacterial resistance.The development of new antibiotics and antibacterial synergists has alleviated the problem.However,this strategy cannot prevent the development of new resistant strains.As of July 1,2020,China has required feed production enterprises to stop producing commercial feed containing antibiotic additives.Therefore,the need is urgent to develop novel antivirulence agents.Anti-virulence agents are one of the most effective means to alleviate bacterial resistance.Anti-virulence agents targets the non-essential life activity processes that lead to bacterial growth,does not easily induce bacterial resistance,and can protect the integrity of the animal’s intestinal flora.At present,there are a variety of clinical antivirulence agents in the development stage around the world that are leading the direction of study in the anti-virulence inhibitor field.The pathogenicity of Salmonella is related to its Type three secretion system(T3SS).T3SS can inject effectors into host cells and interfere with normal host signaling.The T3SS is encoded by SPI-1 and plays an important role during Salmonella invasion of host cells.Effectors secreted by SPI-1,such as SipA,SipC,and SopB can induce the rearrangement of the host cell cytoskeleton,which assists Salmonella invasion of host cells.T3SS has become an ideal target for the development of antivirulence agents.In this study,the Salmonella T3SS(SipA)effectors and the β-lactamase(TEM)reporting system(SipA-TEM)were used to screen T3SS inhibitors from natural compounds by cell infection assays and TEM fluorescence substrate CCF4.After screening compounds,it was discovered that tannic acid can effectively inhibit SipATEM translocation.In vitro drug activity studies showed that tannic acid(16 μg/m L)can significantly inhibit the adhesion and invasion of Salmonella.The secretion,expression,transcription of T3SS related protein in Salmonella were analyzed by traditional molecular biological methods.It was discovered that tannic acid inhibited the DNA-binding ability of HilD to the hilA and invF promoters.Therefore,T3SS could not express and secrete effectors.In vivo therapeutic results showed that tannic acid can effectively prolong the survival time of Salmonella infection model,alleviate pathological damage caused by Salmonella infection,reduce the bacterial load in Salmonella infection model and reduce the inflammation level of cecum tissue in infected mice.Furthermore,the intestinal contents of the mice was analyzed by 16S rDNA high-throughput sequencing,and it was discovered that tannic acid effectively enriched the number of microbial species and reduced Salmonella colonization in the intestine.In conclusion,based on the importance of T3SS of Salmonella during invasion of host cell.This study screened T3SS inhibitors from natural compounds and discovered that tannic acid can inhibit SipA-TEM translocation and further elucidated it’s molecular mechanism of Salmonella invasion of host cell.Simultaneously,the therapeutic effect of tannic acid on Salmonella infection model was systematically evaluated.This study provides lead compounds with a clear mechanism of action for the research and development of Salmonella anti-virulence agents and provides an important theoretical basis for the prevention and control of Salmonella infection.