中文摘要：

本文旨在研究紫色达利菊（purple prairie clover,PPC）对肉牛瘤胃和大肠中大肠杆菌生长的体外抑制作用及其缩合单宁（condensed tannins,CT）对大肠杆菌的抑制机理。体外模拟肉牛瘤胃和大肠环境,以非致病性大肠杆菌ATCC 25922和致病性大肠杆菌O157：H7作为试验菌株,在分别以PPC和苜蓿（无CT,对照）为底物培养,在培养0、1.5、3.0、6.0、24.0 h测定菌落数;以大肠杆菌ATCC 25922为研究模型,分别以添加PPC的CT和红豆草的CT的菌悬液与邻-硝基苯-β-D-半乳糖苷溶液混合,同时以无CT添加的菌悬液和双蒸水混合作为对照,分别在0、40、80、120、160 min时测定β-D-半乳糖苷酶水解产物邻-硝基苯酚的量,以判断细胞内膜通透性的变化;同时观测不同p H（5.3、6.8、7.4、8.0、9.0）和环境温度（4、22℃）对CT作用效果的影响。结果表明：1）与苜蓿相比,PPC对瘤胃（6.0、24.0 h）和大肠中（1.5-24.0 h）的大肠杆菌生长均有显著抑制作用（P〈0.05）。2）CT能够提高邻-硝基苯酚的量;与红豆草CT的作用规律有所不同,PPC的CT的作用会受到温度和p H的影响。结果提示,PPC在瘤胃及大肠环境下均具有抑制大肠杆菌生长的作用,其所含CT抑制大肠杆菌生长的机理部分与其增加细胞内膜的通透性有关,且细胞内膜通透性受到生长环境,如温度和p H的影响。

英文摘要：

This experiment was conducted to evaluate inhibiting effects of purple prairie clover（ PPC,Dalea purpurea Vent.） on Escherichia coli（ E. coli） growth prevalence in the rumen and large intestine and its condensed tannins（ CT） antibacterial mechanism. Ruminal and large intestinal environments were simulated in vitro,non-pathogenic E. coli ATCC 25922 and pathogenic E. coli O157∶ H7 were used as test strains,and the strains were cultured with PPC and alfalfa（ no CT,control） as substrates,respectively. Bacteria number was determined after cultured for 0,1.5,3.0,6.0 and 24.0 h,respectively. W ith the E. coli ATCC 25922 as test model,the bacteria suspensions supplemented with CT from PPC and sainfoin were mixed with o-nitrophenyl-β-D-galactoside（ ONPG） solution,meanwhile,the mixture of bacteria suspension without CT and dd H2 O was used as control. O-nitrophenyl amount,the hydrolysis product of β-D-galactosidase,was determined after cultured for 0,40,80,120 and 160 min,respectively,to analysis the change of cell inner-membrane permeability. The effects of different p H and temperatures on CT actions were also observed. The results revealed as follows： 1） compared with alfalfa,PPC had significant inhibiting effect on growth of E. coli from rumen（ 6. 0and 24.0 h） and large intestine（ 1. 5 to 24. 0 h）（ P〈 0. 05）. 2） CT significantly increased o-nitrophenyl amount（ P〈 0.05）; differently from actions of CT from sainfoin,actions of CT from PPC were affected by p H and temperature. The results indicate that PPC showed inhibiting effect on E. coli growth in bovine rumen and large intestine in vitro incubation; its CT can increase inner membrane permeability of E. coli,however,action of inhibition associated with temperature and p H.