| Elephantopus scaber Linn is a kind of traditional Chinese herbal medicine which is widespread and abundant. The present studies found that lactones are the primary pharmacological effective compounds of E. scaber. Our laboratory has preparaed injection from E. scaber according to the chemical properties of the lactones, and found that the E. scaber injection showed markedly curative effects in chickens infected with Escherichia coli. Nevertheless, there has not been reported about the antibacterial effects and the mechanism of the purified extract of lactones from E.scaber (PELES) so far.Taking the analyses of chemical constituents of E.scaber as the first step, the crude extract from E.scaber was prepared with 80% (v/v) ethanol and followed by purification with silica gel column chromatography and crystallization in this thesis. More importantly, the PELES was detemined and identified by a novel way of thin layer chromatography (TLC) and the antibacterial effects in vitro and the antibacterial mechanism were studied, respectively. The main findings of the thesis were as follows:1. It was found by subentry extracting trial in cuvette and round paper chromatographic trial, that the whole plant of E. scaber herb contained lactone, amino acids, polysaccharide, saponins, naphtha, organic acid, sterol, triterpene, cardiac glycoside, coumarin, flavone, naphthol but no alkaloid and anthraquinone.2. The PELES was determined and identified by TLC, with the developing solvent of petroleum ether (60℃～90℃)︰chloroform︰ether = 3︰5︰2 and the colour developing agent of Ferrum hydroxamic acid, and four specific spots were found with the volumes of Rf at 0.16, 0.33, 0.64 and 0.85, respectively.3. The bacteriostatic test in vitro of PELES was conducted by agar diffusion test, and the results showed that 2.0 mg/mL of PELES inhibited the growthes of Pasteurella multocida (PM) and Bacillus cereus (BC) (P<0.05) and significantly inhibited the growthes of Staphylococcus aureus (SA), Salmonella enteritidis (SE) and Colibacillosis in chicken (CC) (P<0.01), respectively, that PELES at 10 mg/mL and 50 mg/mL significantly inhibited the growthes of all the five strains of bacteria used (P<0.01), that the minimum inhibitory concentrations (MIC) of PELES was 0.313 mg/mL on SA and SE and 0.156 mg/mL on PM, 0.625 mg/mL on CC, and 1.25 mg/mL on BC, and that the minimum bactericidal concentrations (MBC) of PELES on BC was 2.5 mg/mL while the MBC on the other four bacteria used was 0.625 mg/mL.4. As to the effect of temperature to the antibacterial activity of PELES, it was found that PELES was a kind of low heat-resistent substance when the ambient temperature was above 60℃, the antibacterial activity became rather poor.5. With regard to the relationship among the concentration of PELES-time-antibacterial effect, it was found that the key factor influencing the antibacterial effect of PELES was the concentration of PELES. I.e., half MIC of PELES showed antimicrobial effect but maintained a shorter period. And 1 or 2 times of MIC of PELES kept longer inhibition effects, respectively, while 2 times of MIC of PELES sterilized the bacteria used.6. It was found by the test of the impact of PELES on the bacterial growth curve, that PELES suppressed the logarithmic growth of the bacteria, respectively, which means that the bacterial proliferation was inhibited.7. The observation of the affects of PELES to the bacterial ultrastructure by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the killing mechanism of PELES onto bacteria was to destroy part of the cell wall and the membrane permeability of the bacteria, leading to the loss of the bacterial cellular components, proten denaturalization and bacterial autolysis induced by release of lysozymei...
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