Synergistic Effect Of α-helix Antimicrobial Peptides Combine With Traditional Antibiotics Against Bacteria In Vitro And In Vivo

As is known to all, with the overuse of antibiotics and the emergence ofantibiotic-resistant bacteria, the anti-infective therapies become more complicated anddifficult. Traditional antibiotics cannot meet the requirements of treatment, moreover,the research and development of novel antimicrobial drugs cannot keep in pace withthe appearance of infectious diseases caused by pathogens. Therefore, more and morepeople pay their attention to develop new antimicrobial agents and take an active partin investigating new antibacterial treatments.Antimicrobial peptides (AMPs) are small peptides with broad-spectrumantibacterial activity. With further study, people found them exist widely in nature,such as viruses, bacteria, amphibians, insects, higher plants, animals and even humans.AMPs have a great inhibiting and killing effect against Gram-positive bacteria,Gram-negative bacteria and fungi. Some antimicrobial peptides are also used to killprotozoa, virus and tumor cells in vivo, thus, they are a highly promising class ofpolypeptide antibiotics. However, AMPs are unstable and have a higher toxic sideeffects in vivo, therefore, they are limited to be used in clinical application. Thoughthe antimicrobial peptides as drug candidates still have severe difficulties used inclinic, people are trying to explore the optimum conditions. Currently, in the study ofnew treatment, people indeed have made some progress. The combination ofantibiotics means two or more antibacterial agents were used in the treatmentsimultaneously. Combination therapy can expand the scope of antibacterial, delay thedrug resistance and reduce toxic side effects. In the previous studies, antibioticscombination therapy has been successfully used to improve therapeutic efficacy.While, little is known about the combination therapy of antimicrobial peptides andtraditional antibiotics. The purpose of the present study is to evaluate the drugcombination therapy of antimicrobial peptides and traditional antibiotics and to knowif their combination can improve the antimicrobial activity and reduce the toxic sideeffects simultaneously, at the same time, to investigate their action mechanisms.Firstly, we used solid phase peptide synthesis method to synthesize six sequencesof peptide that are used in this study. Then, in order to evaluate their therapeuticefficacy in vitro, we determined the antibacterial activity of antimicrobial peptides andtraditional antibiotics (imipenem, cefepime, levofloxacin hydrochloride and vancomycin) by checkerboard method, respectively. The data showed that theminimum inhibitory concentration (MIC) of antimicrobial peptides were usuallylower than traditional antibiotics, which was consistent with previous study.Secondly, the synergistic effect of antimicrobial peptides combined withtraditional antibiotics against bacteria can be determined by checkerboard method. Inthe study, we selected three Gram-positive bacteria and three Gram-negative bacteria.The results showed that there was a significant synergy between antibiotics andantimicrobial peptides and no antagonism between them.Finally, based on the results of in vitro, we preferentially selected the PL-5andlevofloxacin hydrochloride as candidate drugs in vivo. In order to determine thesynergistic effect of traditional antibiotics and antimicrobial peptides, a topical woundmouse model infected by S. aureus was created. The results showed that there was asignificant synergy between them. Since the action mechanism of antimicrobialpeptides is different compared with that of traditional antibiotics. The strongsynergistic effects between peptides and traditional antibiotics in vitro and in vivosuggest that their mode of actions is complementary.In this study, we can determine that the therapeutic efficacy of the combinationbetween antibiotics and antimicrobial peptides can be used in the treatment ofinfection in the future.