Study On The Control Of Antimicrobial Lipopeptide Against Salmonella Typhimurium

Salmonella typhimurium is a non typhoid serotype of Salmonella.It has a wide host spectrum and can cause diseases of human,livestock or wild animals.It is a pathogen that seriously endangers the development of aquaculture The main clinical symptoms were self limiting gastroenteritis,watery diarrhea,vomiting,abdominal pain and fever.At present,the prevention and control of the disease still depends on antibiotics,but a large number of irrational drugs in animal husbandry have led to the rapid rise of Salmonella drug resistance.The lipopeptide produced by Bacillus subtilis has significant bacteriostatic effect.Due to its special sterilization mechanism,it is not easy to produce drug resistance and has less damage to the original structure.It has the potential to be developed into antibiotics.At present,lipopeptides are mainly used in the prevention and control of plant pathogens,but the inhibitory effect and dosage of animal pathogens are not very clear.Therefore,this study intends to conduct in-depth research based on the characteristics of lipopeptides,evaluate the anti-Salmonella typhimurium effect of lipopeptides in vitro and in vivo,and explore their action mechanism and development potential.The results of this study are as follows:1.Preparation of lipopeptideLipopeptide was purified by acid precipitation.The content and surface activity of surfactin were verified by mass spectrometry and oil drain ring method.According to the growth curve and time yield relationship of Bacillus subtilis,the optimal fermentation time was 48 h;The MIC and MBC of lipopeptide against Salmonella typhimurium were 0.625mg/m L and 1.25 mg/m L respectively.2.Bacteriostatic effect of lipopeptide in vitroThe MBC concentration of lipopeptide can kill all Salmonella typhimurium within 6 h,which is time concentration dependent.0.20 mg/m L lipopeptide can inhibit Salmonella typhimurium infection of BHK-21 cells,and the inhibition rate is as high as 95%.The drug used within 3-5 hours before Salmonella typhimurium infection also has a certain inhibitory effect on the infected cells of bacteria.However,the inhibitory effect on intracellular Salmonella was not obvious.High concentration lipopeptide kills bacteria and low concentration inhibits Salmonella typhimurium infection cells.3.Lipopeptide sterilization mechanism.Lipopeptides had no significant inhibitory effect on the motility and biofilm of Salmonella.The results of transmission electron microscope showed that bacteriostatic lipopeptide caused the leakage of bacterial contents and the disintegration and death of bacteria by destroying the structure of Salmonella membrane.4.Antibacterial activity of lipopeptide in vivoThe anti-Salmonella effect of lipopeptides in vivo was detected through the mouse model of Salmonella typhimurium infection.Lipopeptide can improve the survival rate of mice in the experimental group by 40%,and significantly reduce the amount of Salmonella infection in liver and peritoneum.To sum up,the experiment proved that lipopeptide has antibacterial activity in vivo and in vitro.In vitro tests showed that lipopeptides had significant sterilization and inhibition effects on Salmonella typhimurium.In vivo experiments show that lipopeptide can improve the survival rate of infected mice and reduce bacterial infectivity,which provides a theoretical basis for the development of antibiotic substitutes and clinical medication.