Study On Antimicrobial Activity Of Extracts From Leaves Of Three Species Of Michelia Linn.

Antimicrobial activity of extracts from leaves of Michelia maudiae Dunn, Michelia chapensis Dandy and Michelia platypetala Hand was studied in the paper. The stability of extracts was detected. The extracting technology of active substances was optimized. At the same time, components of antimicrobial activity substances were determined preliminarily. The correlation between total phenols ratio and antimicrobial activity from leaves of three species of Michelia Linn. at different stages was studied. The main results were as follows:(1) The antimicrobial activity of extracts from leaves of three species of Michelia Linn. was studied by agar diffusion method and plate dilution method, and antimicrobial zone diameters and values of the minimal inhibitory concentration were determined. The result indicated that the extracts showed better inhibition to the experimented bacteria, but proved weak antimicrobial effect to microzyme and ineffective against mould. The stability of antimicrobial activity compounds to acid-alkali, heat and ultraviolet was studied with Escherichia coli and Staphylococcus aureus. The result showed that extracts had better inhibition under the acidic and neutral conditions. Temperature and ultraviolet radiation had no influence on the antimicrobial activity of extracts.(2) The extracts with different pretreatment showed different antibacterial activity. The extract of dried powder had better antibacterial activity. The extracts with different solvent had larger differences on the same bacteria, in which 70% ethanol was the best solvent for extracting. Different extraction had larger influence on the antimicrobial activity of extracts, in which ultrasonic extraction was the best method. Take M. maudiae as representative, the optimum extraction condition of antimicrobial activity substances determined by orthogonal test in the basis of single factor experiment was as follows: the concentration of ethanol was 70%; the ratio of material and solvent was l:30; extraction temperature was 65°C ; extraction time was 30minutes with 2 times.(3) The ethanol extracts of three species of Michelia Linn. were extracted with petroleum ether,Chloroform , ethyl acetate, n-butanol and water in turn. The antimicrobial activity of the various components was tested. It was indicated that the two components extracted from Chloroform and ethyl acetate had better inhibition effect. The two components were protested preliminaryly by means of tube-test and thin layer chromatography (TLC). It was indicated that there were phenols, flavonoids, coumarins, tannins and terpenes in the leaves of three species of Michelia Linn..(4) The content of total phenols of ultrasonic extracts at different stages (May, July, September and December) were determined and the antimicrobial activity to bacteria was studied. The results showed that the content of total phenols was different obviously at different stages. The antimicrobial activity at different stages was also different. And The antimicrobial activity had some correlation with the content of total phenols.