Antibacterial Mechanism Of Broad-spectrum Antimicrobial Peptide MPX And Research On Skin Wound Repair

As the body’s first line of defense,the skin prevents harmful substances or microorganisms fromentering the body.When the normal skin barrier is disrupted and cellular immunity is suppressed,pathogenic bacteria can colonize wounds and cause infection.Healing of skin infections is an organized process.Although the infiltration of immune cells such as macrophages or leukocytes at the infection site prevents the initial microbial infection,antibiotics are unavoidable to accelerate the healing process.However,treating such wounds has been challenging due to the emergence of antibiotic-resistant strains.Staphylococcus aureus is a Gram-positive pathogen that is widely distributed in the surrounding environment and is highly susceptible to drug resistance.Therefore,wounds on the skin surface are easily infected by Staphylococcus aureus,which eventually leads to skin diseases such as cellulitis.Antimicrobial peptides（AMPs）have the advantages of good water solubility,strong thermal stability,broad antibacterial spectrum,wide sources,etc.,and are not easy to develop drug resistance,so they are considered as one of the best potential substitutes for antibiotics.This research mainly focuses on the antimicrobial peptide MPX and Staphylococcus aureus,as follows:In this study,the antimicrobial activity detection and bactericidal kinetics of the antimicrobialpeptide MPX against Staphylococcus aureus ATCC 25923,Escherichia coli ATCC 25922,Salmonella CVCC 541,and Candida albicans ATCC 90029 were carried out.The results showed that MPX had good antibacterial activity against the above four strains,especially against Escherichia coli,the MIC was as low as 15.625μg/m L.The results of bactericidal kinetics showed that MPX had good bactericidal activity against the above four strains,and MPX with 4 MIC could kill 99.9%of viable cells within 1 h.The results of the study on the bactericidal mechanism of antimicrobial peptides found that MPX can destroy the membrane integrity,increase the membrane permeability,and change the electromotive force of the membrane,thereby allowing the contents to leak out and mediating bacterial death.In addition,the results of biofilm formation assay showed that MPX could also inhibit the formation of bacterial biofilm.The results of the stability study of antimicrobial peptides found that MPX has stability to some salt ions,good acid-base stability,thermal stability and repeated freeze-thaw stability.The above results indicate that MPX has good antibacterial activity and broad-spectrum antibacterial potential,and is expected to be an effective substitute for traditional antibiotic therapy.The therapeutic effect of antimicrobial peptide MPX ointment against Staphylococcus aureuswound infection was evaluated on the mouse skin open scratch model.Mice were infected with Staphylococcus aureus ATCC 25923 at 2.5 x 10~9CFU.One day after bacterial colonization and infection,MPX ointment was applied for treatment,as the MPX ointment treatment group.The results of the study found that MPX cream could reduce the colonization of Staphylococcus aureus on the wound surface and accelerate the healing speed of the skin wound in mice.The results of skin HE staining,cell ultrastructure and immunohistochemistry showed that MPX cream could promote the repair of wound skin,reduce the infiltration of inflammatory cells,and reduce the level of wound inflammation.In addition,MPX ointment was able to reduce lung damage caused by Staphylococcus aureus infection.The above results show that MPX ointment can reduce the colonization of wound skin and promote wound healing,which provides a research basis for the research and development of new antibacterial preparations.The mouse acute occlusive infection model was used to evaluate the therapeutic effect of MPXafter acute infection of subcutaneous tissue by Staphylococcus aureus.Mice were infected subcutaneously with Staphylococcus aureus ATCC 25923 at 1.25 x 10~8CFU.Two hours after bacterial infection,MPX was injected or MPX ointment with different active contents was applied for treatment.The results of the study found that MPX was able to promote tissue repair in Staphylococcus aureus infection.In addition,the results of skin HE staining showed that MPX treatment facilitated the formation of appropriate abscesses at the subcutaneous infection site and facilitated the clearance of bacteria by the skin immune system.The above results show that MPX can effectively resist the invasion of subcutaneous tissue by Staphylococcus aureus,and MPX has the potential to become an immune preparation,providing new thinking and paths for the immunotherapy of bacterial infections.