| Due to the abuse of antibiotics,the number of drug-resistant bacteria is increasing,which seriously threatens the health of the public.During the period 2010-2016,the Chinese bacterial resistance monitoring network detected that Acinetobacter occupies a relatively high proportion,with a detection rate of 10.76%.Acinetobacter Baumannii(AB)is a Gram-negative bacterium.The infection of this bacterium is more common in hospitals.Acinetobacter baumannii is easy to set on the surface of the human body exposed to the outside world.After colonization of these sites,it is easy to cause infection of the respiratory tract,sepsis,urinary system,and surgical wounds.Due to the increasing prevalence of antimicrobial drugs,the number of drug-resistant Acinetobacter baumannii has increased in recent years.In the survey statistics of the World Health Organization,every year,due to the wound infection,there are many deaths.Data research shows that in clinical patients with traumatic infection,the common pathogen of infected patients is Acinetobacter baumannii.In recent years,fully resistant Acinetobacter baumannii has emerged,which makes the treatment of diseases caused by Acinetobacter baumannii become more and more difficult.Therefore,finding new anti-Acinetobacter baumannii drugs is imminent.Antibacterial peptide(AMP)is a short peptide with many structures.It has a small molecular weight and wide biological activity,and is resistant to bacteria and fungi,anti-virus and anti-inflammatory.Because cyclic peptides have the characteristics of low toxicity,easy penetration of cell membranes,and low enzymatic hydrolysis,cyclic peptides have better biological activity and stronger medical value than linear peptides.Based on the good characteristics of cyclic peptides,in recent years,people have become more and more interested in the research of cyclic peptides,and cyclic peptides are expected to become a class of drugs with great potential against bacterial diseases.This subject aims to design a new antibacterial cyclic peptide,study its activity and stability and safety,conduct a preliminary exploration of its mechanism,and study its therapeutic effect on the infection of multi-drug resistant Acinetobacter baumannii after early skin trauma in rats.The results achieved are as follows:1.The research group chose bovine lactoferrin as the research template in the early stage.Bovine lactoferrin is LfcinB64-9(RRWQWR).A series of hexapeptides were designed.29 antimicrobial peptides with similar structure were found in the literature.3D-QSAR model was established through computer-aided drug design.Based on this model,3 new antimicrobial peptides were obtained.Characteristic synthesis of cyclic peptides,and finally got the 4 antibacterial cyclic peptides needed in this research.2.The designed antibacterial cyclic peptide has an antibacterial effect on the multi-resistant strains of Acinetobacter baumannii and common non-resistant bacteria.It also has good antibacterial activity.Among them,the cyclic peptide P4 has the best antibacterial effect,and the minimum inhibitory concentration MIC for multi-resistant Acinetobacter baumannii is 16 μg / mL,which is close to the in vitro antibacterial activity of imipenem;3.The designed antibacterial cyclic peptide has a higher sterilization speed than the control imipenem,and can kill bacteria at 4 hours;4.The four cyclic peptides and imipenem have the synergistic effect of combined medication,and the graded antibacterial concentration(FIC)index is ≤0.55.In salt solutions of different concentrations,NaCl and CaCl2 solutions were selected in this experiment.Cyclic peptides P1 and P4 still have good antibacterial activity.At low concentrations,the antibacterial activity in both salt solutions is above 95%.At a high concentration of NaCl and CaCl2 of 36 mg / mL and 1 mg / mL,the antibacterial activity was also above 80%.The other two cyclic peptides are easily degraded in high-concentration CaCl2 solution and lose antibacterial activity.The stability of the cyclic peptide P4 was tested for plasma stability,and it was found that the cyclic peptide P4 will not be degraded during the reaction with sheep plasma in different time periods,and it has better stability,and the content is higher than 80%;6.The four cyclic peptides have low cytotoxicity to two normal cells HLF-1 and HaCaT at low concentrations,the cell value-added inhibition rate is less than 15%,and the cyclic peptide P4 has low hemolytic toxicity.Under the condition of 256μg / mL,it is still less than 5%,and the other three cyclic peptides have high hemolytic toxicity.7.Cyclic peptide P4 has a certain therapeutic effect on the early treatment of rat skin with multi-drug resistant Acinetobacter baumannii,which is significantly higher than that of the normal saline control group.The effect of antimicrobial peptides in the high concentration group was close to that of the control sulfamilon,but the dosage was lower than that of sulfamilon.The four antibacterial cyclic peptides designed in this study all have a certain antibacterial activity,and imipenem has a synergistic effect of combined medication.Cyclic peptide P4 has the best antibacterial effect,the lowest bacteriostatic concentrationis closest to the control imipenem,has a higher sterilization rate,lower hemolytic toxicity and cytotoxicity,and better salt stability and plasma stability.At the same time,cyclic peptide P4 has a certain antibacterial effect on the early skin wound infection of rats with multi-drug resistant Acinetobacter baumannii. |
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