Studies On Screening Of Antibacterial Activities Of Several African Medicinal Plants

In order to screen for plant resources with good antibacterial effects,a variety of medicinal plants both grown in China and Africa were collected to test their antibacterial activity against some common mircobial pathogens in this study.A number of different medicinal plants were crushed and powdered,then soaked and extracted with ethanol for further screening.The extract solution was concentrated under reduced pressure to yield the extract syrup.The syrup was further processed via low-temperature freeze-drying to obtain crude extract,and micro-fold dilution method was then used for the activity screening.The antibacterial activity of ethanol extracts of medicinal plants against Staphylococcus aureus,Escherichia coli and Salmonella enterica was measured in a 96-well plate.In order to further subdivide the categories of antibacterial active components,those crude extracts were sequentially partitioned with petroleum ether,dichloromethane,ethyl acetate,and n-butanol,and then subjected to vacuum concentration and low-temperature freeze-drying,which were employed to test the antibacterial activity of different extraction parts of each plant for Staphylococcus aureus,Escherichia coli and Salmonella enterica.Among all of the tested medicinal plants,Cedrelopsis grevei collected from Madagascar showed excellent antibacterial activity against Staphylococcus aureus.The minimum inhibitory concentration(MIC)of the crude extracts of Cedrelopsis grevei on Staphylococcus aureus was 32 μg/mL,and the minimum inhibitory concentration(MIC)of the petroleum ether fraction on Staphylococcus aureus was 4 μg/mL.The MIC values of the methylene chloride extract of Cedrelopsis grevei against Staphylococcus aureus and Escherichia coli were 128 μg/mL and 512 μg/mL,respectively.In order to study the composition of antibacterial active ingredients,the petroleum ether fraction of Cedrelopsis grevei was analyzed by gas chromatography-mass spectrometry(GC-MS).The major results of this study are summarized as follows:(1)Twelve medicinal plant extracts with significant antibacterial activities were screened out in the present study,of which 11 are from Africa and one is from Fujian,China.The MIC of these 12 extracts ranged from 4 to 512 μg / mL.(2)The GC-MS analysis of Cedrelopsis grevei petroleum ether extract with the most potent antimicrobial activity revealed that: Cedrelopsis grevei petroleum ether extract mainly contains 5 major types of chemical components,including 42 compounds,of which the relative percentage content of sesquiterpenes were accounted for 95.15%,terpenes accounted for 2.80%,benzene derivatives accounted for 0.68%,alkyl esters accounted for 0.27%,and enynes accounted for 0.76%.Sesquiterpene compounds consisted of sesquiterpene hydrocarbons and sesquiterpene oxygenated derivatives,which accounted for 32.69% and 62.46% of the total component content,respectively.Among the petroleum ether fraction of Cedrelopsis grevei,β-eudesmol accounted for 30.65%,cubenol accounted for 10.98%,β-selinene accounted for 7.94%,hinesol accounted for 5.41%,viridiflorol accounted for 4.53%,α-guaiene accounted for 3.07%,Naphthalene,1,2,3,4,4a,5,6,8a-octahydro-4a,8-dimethyl-2-(1-methylethenyl)-,[2R-(2α,4aα,8aβ)] accounted for 2.81%,α-muurolene accounted for 2.27%,α-longipinene accounted for 2.22%,naphthalene,1,2,3,5,6,8a-hexahydro-4,7-dimethyl-1-(1-methylethyl)-,(1S-cis)accounted for 1.83%,caryophyllene oxide accounted for 1.77%,aromadendrene was 1.59%,tricyclo [4.4.0.0(2,7)] dec-3-ene-3-methanol,1-methyl-8-(1-methylethyl)accounts for 1.47% and α-bisabolol accounted for 1.46%.Caryophyllene oxide,β-caryophyllene,germacrene D,viridiflorol,aromadendrene,and α-bisabolol are the sesquiterpenes that have been determined to show antibacterial activities in the petroleum ether extract of Cedrelopsis grevei.Aromadendrene is a highly lipophilic sesquiterpene hydrocarbon that can destroy the fluidity of bacterial cell membranes.Sesquiterpenoids may be the main bacteriostatic active components of Cedrelopsis grevei petroleum ether extracts due to their significant bacteriostatic activity.African medicinal plants have great potential for screening antibacterial active ingredients,and these plants are worthy of further study.