Caffeic Acid And Caffeic Acid Nanoparticles Promote Antibacterial Effect Of H₂O₂

Background:Bacterial infectious diseases are a serious threat to human economy and future development.Currently,antibiotic antibacterial drugs are usually used for clinical treatment,but the unregulated use or even abuse of antibiotics has caused problems such as bacterial resistance.Therefore,it is of great practical importance to develop new non-antibiotic antibacterial agents.H₂O₂,as a widely used medical cleansing and wound disinfectant,requires a high concentration of H₂O₂（3%）to achieve the desired antibacterial effect,and has disadvantages such as oxidative damage to normal tissue skin and delayed healing rate.Caffeic acid is a natural polyphenolic compound with biological activities such as anti-inflammatory,antioxidant and antibacterial.The antibacterial properties of H₂O₂enhanced by caffeic acid and the antibacterial effect of H₂O₂promoted by caffeic acid delivery system-caffeic acid nanoparticles were examined.Methods:Determination of caffeic acid and caffeic acid nanoparticles combined with H₂O₂for Gram-negative bacteria Escherichia coli（E.coil）and Gram-positive Staphylococcus aureus（S.aureus）by coating plate method,dilution counting method,viable bacteria counting method,MTT method and ultraviolet spectrophotometry for in vitro antibacterial studies.The biocompatibility evaluation of caffeic acid nanoparticles to human umbilical vein endothelial cells was tested by crystal violet staining method.Results:（1）Experimental study on the antibacterial effect of caffeic acid combined with H₂O₂:（1）Only when H₂O₂is 1.2 mmol/L,it has a bactericidal effect on E.coil;when the concentration of caffeic acid is as high as 5 mmol/L,it has almost no antibacterial activity on E.coil.However,0.2 mmol/L caffeic acid combined with 0.2 mmol/L H₂O₂has significant antibacterial activity against E.coil,and there is a significant difference.（2）12 mmol/L H₂O₂has no obvious antibacterial effect on S.aureus;4.8 mmol/L caffeic acid has almost no antibacterial activity on S.aureus.And the combination of nearly 5 mmol/L caffeic acid and 8 mmol/L H₂O₂has almost no antibacterial effect on S.aureus.（2）Experimental study on the antibacterial effect of caffeic acid nanoparticles combined with H₂O₂:（1）The average particle size of the caffeic acid nanoparticles is 279.5 nm,and the nanoparticle size distribution is narrow,the dispersion is good,and the particle size distribution diagram is single peak.All show negative charge,Zeta is-9.64 m V.The particles are distributed like spherical particles.（2）As low as 1 mmol/L H₂O₂does not cause any damage to S.aureus;100μg/m L caffeic acid nanoparticles also does not cause any damage to S.aureus;however,1mmol/L H₂O₂combined with 80μg/m L caffeic acid nanoparticles Compared with the control group,the particles have obvious antibacterial effect on S.aureus.（3）As low as 0.2 mmol/L H₂O₂does not cause any damage to E.coi;100μg/m L caffeic acid nanoparticles also does not cause any damage to E.coi;however,0.2 mmol/L H₂O₂combined with 80μg/m L caffeic acid nanoparticles The particles have strong antibacterial activity against E.coi.（4）The biosafety of caffeic acid nanoparticles in vitro is good.Conclusion:Caffeic acid was able to promote the antibacterial activity of H₂O₂against E.coil;however,it had almost no antibacterial effect on S.aureus.Caffeic acid nanoparticles were able to enhance the antibacterial effect of low concentration of H₂O₂on S.aureus and E.coil.Caffeic acid nanoparticles were not cytotoxic.