| Staphylococcus epidermidis is one of coagulase-negative staphylococci.It is a common bacterium presented in the skin,vagina and other parts of hunman.It belongs to conditional pathogens that could cause bacteremia,pneumonia,skin infections and other diseases under certain conditions.The bacteria could easily cause persistent infections in patients with weakened immunity and implanted medical devices.Although the virulence of S.epidermidis was usually low,the bacteria could easily form stubborn biofilm,which can prevent the body's immune system and antibiotics,increasing the difficulty treatment of infection.At the same time,due to the non-standard use of antibiotics,the drug resistance of S.epidermidis had become increasing serious,which had brought tremendous challenges to antibiotic therapy.In summary,there is an urgent need to develop drugs which have new mechanisms of action to against S.epidermidis and biofilms.Lysin is a cell wall hydrolase encoded by phage at the end of bacteriophage cycle infection which target is peptidoglycan of the cell wall.It could kill the bacteria specifically and efficiently by destroying the integrity of the cell wall.In the previous study,S.aureus bacteriophage lysin Lys GH15 had showed a broad-spectrum,high-efficiency antibacterial effect against S.aureus in vivo and in vitro.So,whether Lys GH15 could kill S.epidermidis and eliminate and biofilm?In order to answer this scientific question,this paper carried out a series of related studies.Firstly,we isolated and identified 25 strains of S.epidermidis,17 strains of S.aureus,2 strains of Staphylococcus hominis,and 2 stains of Staphylococcus haemolyticus from clinical samples.The antibacterial activity of LysGH15 against those strains were further tested by plaque assay and colony count.The results showed that LysGH15 expressed significant antibacterial activity against all those strains at concentration of 20?g/m L,the bacteria were decreased 4 log units.LysGH15 was repeatedly applied to S.epidermidis,strains were still sensitived to Lys GH15.The results indicating that the bacteria did not develop resistance to LysGH15.Lys GH15produced specific antibodies against LysGH15 in vivo,specific antibodies only slowed down the antibacterial activity of LysGH15 against S.epidermidis in vitro,did not effect its ultimate antibacterial.The effects of LysGH15 on biofilm formation of S.epidermidis,S.aureus,S.hominis,and S.haemolyticus were investigated in further experiments.A 96-well microtiter plate method was used to screen out the strains with strong biofilm formation ability.The effective concentrations of Lys GH15 on inhibiting the formation of biofilms and eliminating the formed biofilms were determined by using crystal violet staining,scanning electron microscopy,and laser confocal microscopy assays.The results were confirmed that LysGH15 could effectively inhibit the formation of biofilms at a concentration of?50?g/mL,and that the formed biofilms could be effectively eliminated at a concentration of?100?g/m L.In vivo experiments showed that S.epidermidis B020 strain could cause infection in mice which had an intraperitoneal attack of 1×10~8 CFU/mouse.The model was used to evaluate the therapeutic effect of Lys GH15.The results showed that Lys GH15 could effectively treat mice at a dose of 20?g/mouse which infected with S.epidermidis in infection.Compared with the control group,Lys GH15 could significantly improve the health of mice,meanwhile,it reduced the bacteria loads in blood and organs,and reduced the level of IFN-?,TNF-?,IL-6 cytokines,and significantly reduced the pathological changes of tissues and organs.The above studies showed that Lys GH15 had a broad-spectrum and high-efficiency antibacterial activity against S.epidermidis.LysGH15 could effectively prevent biofilm formation and eliminate formed biofilm by S.epidermidis,S.aureus,S.hominis and S.haemolyticus.Therefore,Lys GH15 showed good application prospects in the treatment of S.epidermidis infections and elimination biofilms. |
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