Study On Antibacterial Activity And Antibacterial Mechanism Of A Caffeic Acid Derivative(ZZJ) Of Echinacea

Echinacea is a kind of "foreign herbal medicine" with many kinds of medicinal active components.It has been introduced and cultivated in many areas in China and has been listed in the list of Agricultural Plant varieties Protection of the people’s Republic of China(11th batch).Echinacea has anti-oxidant,anti-inflammatory,immune enhancement,antibacterial and other pharmacological effects,among which caffeic acid and its derivatives are the main antibacterial active components.However,the number and type of caffeic acid derivatives are complex,and the specific antibacterial mechanism of each monomer is not clear.In this study,the antibacterial activity and mechanism of caffeic acid derivatives from Echinacea purpurea were studied.The results are as follows:1.The antibacterial activity of caffeic acid derivative ZZJ against various pathogenic bacteria was determined by disk diffusion method.It was found that ZZJ had antibacterial activity against Staphylococcus aureus,Pseudomonas aeruginosa and Acinetobacter baumannii,while ZZJ had not show antibacterial activity against Escherichia coli producing extended-spectrum β-lactamases(ESBLs).And Klebsiella pneumoniae.The minimal inhibitory concentration(MIC)of ZZJ was determined by 96 microplate dilution method.It was found that ZZJ had the best bacteriostatic effect on methicillin resistant Staphylococcus aureus(MRSA),and its minimum inhibitory concentration against MRSA standard strain(ATCC 43300)was 0.7 mg / m L.2.The effects of different concentrations of ZZJ on the growth of MRSA were measured by automatic growth curve instrument.It was found that ZZJ treatment could inhibit the growth of MRSA,and the inhibitory effect increased with the increasing concentration.3.The antibacterial mechanism of ZZJ on MRSA was investigated by means of morphological,physiological and biochemical methods.The conductivity of MRSA cells treated with different concentrations of ZZJ was measured.It was found that ZZJ with higher than concentration of 0.7mg/ml could increase the permeability of MRSA cell membrane.Scanning electron microscopy(SEM)was used to observe the morphology of MRSA treated with different concentrations of ZZJ.It was found that the morphology of MRSA did not change significantly,but the aggregation of bacteria occurred and the adhesion of bacteria increased after being treated with ZZJ higher than a certain concentration(0.7mg/ml).By analyzing the soluble protein content of MRSA treated with different concentration of ZZJ,it was found that the soluble protein content of MRSA decreased obviously after ZZJ treatment with higher than certain concentration(0.7mg/ml).4.After being treated with different concentrations of ZZJ,the m RNA levels of drugresistant genes were detected.Results showed that the transcriptional levels of mec A and mec R1 were significantly down-regulated at certain concentration(0.7mg/ml).And m RNA level of bla Z and fem A genes were decreased at some content when treated with ZZJ of different concentrations.There was a dose-dependent relationship.In conclusion,ZZJ,a caffeic acid derivative of Echinacea,has a strong inhibitory effect on Gram-positive bacteria,especially on MRSA.ZZJ can increase the permeability of MRSA cell membrane and make the soluble protein leak out of the cell.ZZJ could reduce the transcription level of drug-resistant gene of MRSA to relieve the drug resistance of MRSA.