致仔猪水肿病大肠杆菌减毒株的毒力测定及其在仔猪肠道内增殖的分析

在已构建致仔猪水肿病大肠杆菌S451521菌株的2个毒素敲除菌株（F1、F2）基础上,进一步测定了其毒力及在仔猪肠道内的繁殖能力。选择30日龄的ICR小鼠并随机分成4组,A、B、C试验组分别灌胃接种不同浓度的野生菌株S451521及其毒素敲除菌株F1、F2,D组以灭菌生理盐水作阴性对照;结果表明减毒菌株F1和F2毒力均比野生菌株弱,其中F1株减弱了60.73%、F2株减弱了84.38%。选择24日龄未经仔猪水肿病疫苗免疫过的仔猪共14头,并随机分为2组;第1组口服接种减毒菌株F2,第2组以灭菌生理盐水作阴性对照,定期采集仔猪粪样并进行细菌监测;结果显示,仔猪排出减毒菌株F2的数量随时间不断增多,在接种后28d可达到每克粪样含目的菌约70 000cfu。这说明减毒菌株F2能够在仔猪体内定植并大量繁殖。

Virulence detection and colonization analysis in piglet intestinal tract of attentuated edema disease-causing Escherichia coli

Based on two toxin-gene knocked stains（F1and F2）originated from the wild type edema disease-causing Escherichia coli strain S451521,the virulence and reproductive ability of the 2attentuated variants were further detected in this reseach.Thirty-day-old ICR mice were separated into three experimental groups and one control group.The animals of the experimental groups A,B and C were intragastric inoculated with E.coli S451521,F1 and F2respectively,and the animals of the control group D were treated with normal saline（NS）in the same way.The data showed that the virulence of the attentuated variants,F1 and F2,were all lower than the wild type strain S451521,thereinto,F1 strain reduced by 60.73% while F2 strain reduced by 84.38%.Fourteen piglets,24-day-old and non-immune,were separated into two groups,including experimental groupⅠ were intragastric inoculated with attentuated strain F2 while group Ⅱ were treated with NS as control.Following the fecal samples were collected from all the animals,bacteria were counted and identified.The result showed that the number of E.coli strain F2 defecated from the tested piglets was increased with time,and can achieve 70 000 cfu per gram of feces at 28 dafter inoculation.The data indicate that the attentuated E.coli strain F2 could colonizated and grow abundantly in the piglet＇s intestine.