The Role And Mechanism Of Antimicrobial Peptides(AMPs) Tachyplesin Ⅲ And Cathelicidin BF In Anti-Multi Drug Resistant(MDR) Bacterial Infection

Sepsis is an uncontrolled inflammation that triggers systemic acute organ damage and even life-threatening infections caused by pathogenic bacteria.According to the report by World Health Organization,more than 300,000 people die of sepsis every year.Sepsis is mostly caused by bacterial infections,and some are caused by fungal or viral infections.One of the greatest inventions in the 20th century is the discovery and use of antibiotics.The clinical use of antibiotics has greatly improved the life quality of patients with infectious diseases.However,the abuse of antibiotics has also led to the emergence of resistant bacteria,and even multi-drug resistant(MDR)"super"bacteria.Sepsis caused by drug-resistant bacteria infection not only aggravates the waste of medical resources,but also has a great impact on social and economic development,and more importantly,it seriously affects the lives and health of patients.Therefore,it is imperative to develop effective treatments to control drug-resistant bacteria infection.Antimicrobial peptides(AMPs)are small molecular peptides with antibacterial activity.Most of the antimicrobial peptides have small molecular weights,relatively simple structures,and strong killing ability to bacteria.They construct an important defense line for the host against pathogen infections.The antibacterial function is mainly to destroy the stability of the bacterial membrane and interfer the reproduction of bacteria.A more comprehensive understanding of novel targets,and their interactions with the immune system of AMPs is beneficial to the development of new treatment options for multi-drug-resistant bacteria.in order to obtain new antibacterial target sites and discover mechanisms for the development of drug-resistant bacteria which may lay the foundation for the development of antibacterial drugs,in this study,we screened the antibacterial effects of antimicrobial peptides of different structures and paid particular attention to the antibacterial effects of clinically isolated multi-drug resistant bacteria,.Previously,we have screened the anti-MDR bacterial effects of AMPs with different structures which were reported.We found that the AMP Tachyplesin Ⅲ and Cathelicidin BF possessed good antibacterial effects against multiple clinically isolated MDR bacteria,which have low toxicity and good stability.1)The antibacterial peptide Tachyplesin Ⅲ could effectively destablize bacterial membranes and change the morphology of bacteria.The low dose of Tachyplesin Ⅲ that mainly binds to the genetic material could cause partly death of bacteria and,while the high dose mainly located on the bacterial membrane could kill all the bacteria and.The transcriptome results showed that after Tachyplesin Ⅲ treatment,the synthesis pathway of unsaturated fatty acid in resistant bacteria changed significantly.Further analysis showed that Tachyplesin Ⅲ competitively bind to the enzyme active center of FabG and NADPH,and inhibit its consumption of NADPH that leads to the antibacterial effect.In vivo experiments have shown that mixed multi-drug resistant bacteria infection induced worse clinical manifestations than single drug-resistant bacteria,along with more severe inflammation and higher mortality in mice.Tachyplesin Ⅲ can effectively protect mice from mixed drug-resistant bacteria infection,improve the survival rate of mice,and also effectively enhance the phagocytic ability of macrophages.2)The antimicrobial peptide Cathelicidin BF is not able to completely kill bacteria at a dose of 1/4 minimum inhibitory concentration(MICs),but it can penetrate the cell membrane and act on the internal sites of the bacteria.Further proteomics results indicated that it was involved in the process of transcription.The high-dose treatment of 4 MIC can also damage the membrane integrity of all bacteria to achieve the effect of killing bacteria.This study focused more on the analysis of Cathelicidin BF’s immunomodulatory ability,especially its regulatory effects on the neutrophil extracellular traps(NETs).Cathelicidin BF promoted the formation of NETs in vitro in a dose-dependent manner.In vivo results show that Cathelicidin BF can effectively recruit neutrophils and macrophages to enter the lungs forming an immune defense line.After infected by the drug-resistant bacteria,the neutrophils form NETs structure to capture and kill the bacteria,and the phagocytic ability of macrophages is also enhanced.Under the combined action of the two immune cells,the ability of mice to resist infection by the drug-resistant bacteria is enhanced.The whole process was regulated by autophagy.This study also preliminarily explored the role of RIPK3-MLKL in the process of host resistance to drug-resistant bacteria infection,which was necessary for the formation of NETs.The results of this study revealed for the first time the new targeting site and mechanism of Tachyplesin Ⅲ,as well as the potential for the development of new antibacterial drugs.In addition,we also analyzed the mechanism of antimicrobial peptide Cathelicidin BF by mobilizing the host’s immune system against drug-resistant infections.Our research revealed the antibacterial mechanism of two antimicrobial peptides with different modes of action,suggesting that antimicrobial peptides have promising potential in developing sepsis drugs caused by multi-drug resistant bacteria infection.