嗜酸乳杆菌细胞壁提取物对致病性大肠杆菌粘附鸡肠纹状缘膜的影响

为研究嗜酸乳杆菌细胞壁提取物对致病性大肠杆菌(E.coli)粘附鸡肠纹状缘膜的影响,本实验以雏鸡小肠纹状缘膜为模型,以嗜酸乳杆菌和鸡致病性E.coli O78为研究对象,提取嗜酸乳杆菌表层蛋白、肽聚糖及E.coli O78菌毛,雏鸡小肠纹状缘膜,采用固相粘附试验和生物素标记法从分子间相互作用的关系评价了嗜酸乳杆菌细胞壁提取物对菌毛粘附的抑制作用,结果表明:表层蛋白和肽聚糖对菌毛粘附具有明显的抑制作用,呈浓度依赖性抑制菌毛与纹状缘膜的结合,具有竞争性拮抗作用,这主要是由空间占位造成的。肽聚糖的抑制作用相对较小。     

大肠杆菌O157和其它产志贺毒素大肠杆菌的毒力因子——粘附素

大肠杆菌O157的致病性已引起全世界公众和微生物学家的关注，而O157的致病因子有很多，本文就大肠杆菌O157可能的粘附素：菌毛、OMP及紧密素在致病中的作用进行综合评价，并对这些因子在其它产志贺毒素大肠杆菌中的出现率及与致病的关系进行分析，以期对大肠杆菌O157的致病机理有一个比较清楚的认识，推动我国对大肠杆菌O157的研究，以填补我国在这方面的相对空白。     

Age-dependent competition of porcine enterotoxigenic E. coli (ETEC) with different fimbria genes - short communication

To investigate the association of pathogenic Escherichia coli fimbrial adhesins with the development of diarrhoea in piglets of different age groups and to test their relative competitiveness, piglets were orally inoculated with a mixture of E. coli strains harbouring F4, F5, F6, F18 and F41 fimbrial genes. A total of 537 E. coli strains with haemolytic activity were isolated from 36 diarrhoeic piglets. The F4 fimbrial gene was observed in 98.5%, 97.6% and 80.6% strains carrying fimbrial genes isolated from diarrhoeic piglets that were infected at 1, 3 and 5 weeks of age, respectively. These data demonstrate that F4 fimbriae are highly associated with diarrhoea in piglets of all age groups. Interestingly, the F18 fimbrial gene was observed in 2.4% and 25.4% strains carrying fimbrial genes isolated from the 3- and 5-week-old groups, respectively, which confirms that F18 fimbriae are associated with diarrhoea in piglets from late stages of suckling to post-weaning, and are more related to diarrhoea in weaned than in unweaned piglets.     

Escherichia coli O157:H7 and other Shiga toxin-producing E. coli in white veal calves

The aims of the study were to determine the prevalence of enterohemorrhagic Escherichia coli O157:H7 (EHEC O157) and other Shiga toxin-producing E. coli (STEC) in feces of white veal calves in an operation in Ontario, to evaluate exposure of the calves to EHEC O157, and to investigate the milk replacer diet and antimicrobial resistance as factors that might influence the prevalence of EHEC O157. Feces from three cohorts of 20-21 calves were collected weekly for 20 weeks and processed for isolation of EHEC O157:H7 and detection of STEC by an ELISA. Exposure to EHEC O157 was also investigated by measuring IgG and IgM antibodies to the O157 lipopolysaccharide (O157 Ab) in sera by ELISA. The prevalences of EHEC O157 were 0.17% of 1151 fecal samples and 3.2% of 62 calves, and for STEC were 68% of 1005 fecal samples and 100% of 62 calves. Seroconversion to active IgG and IgM O157 Ab responses in some calves was not associated with isolation of EHEC O157. The milk replacer contained low levels of antibodies to EHEC antigens and without antimicrobial drugs, it did not inhibit the growth of EHEC O157 in vitro. Two E. coli O157:H7 that were isolated were totally drug sensitive whereas 60 commensal E. coli isolates that were examined were highly resistant. Antibodies in milk replacer that might be protective in vivo, and susceptibility to antimicrobial agents in the milk replacer may contribute to the low prevalence of EHEC O157 in white veal calves.     

英国食品标准局发布大肠杆菌预防指南

一、预防指南介绍近日,英国食品标准局发布公告,阐述了食品商店控制食品污染物E.co-li O157风险需要采取的措施.指南主要用于指导食品商店采取措施保护消费者,避免产生大肠杆菌污染事件.许多商店将按照指南中提供的具体步骤执行,同时也提倡各商店采取尽可能的措施预防交叉污染.英国食品标准局也希望各地食品安全主管部门在发挥监管职能时能够采纳本指南中的措施.     

肠出血性大肠杆菌O157：H7噬菌体的分离纯化

分离纯化了抑制肠出血性大肠杆菌（Enterohemorrhagic E coli,EHEC）0157：H7的噬菌体,并对其进行效价测定。将宿主菌EHEC0157：H7培养制成悬液后与污水样品37℃共培养16h,将培养物离心、过滤除菌后得到该菌的噬菌体原液。噬菌体原液采用双层琼脂平板法进行5次纯化,得到直径相同的噬菌斑。纯化后噬菌体的效价达到12×10^pfu。电镜观察表明,该噬菌体呈蝌蚪状。根据ICTV对病毒的分类标准,该噬菌体属长尾噬菌体科,为烈性噬菌体。     

壳寡糖对断奶仔猪回肠养分消化、小肠形态及隐窝细胞增殖的影响

本研究旨在探讨日粮添加壳寡糖对断奶仔猪生长性能、营养物质消化率和小肠功能的影响,评估其作为断奶仔猪日粮中抗生素替代品的效果。试验选择21 d断奶的三元仔猪280头,随机分为5组,每组4个重复,每个重复14头猪,各组猪只分别饲喂在基础日粮中分别添加0、80、160、240 mg/kg壳寡糖和45 mg/kg盐霉素的日粮,试验分为1~28 d和29~56 d两个阶段,共进行8周。结果显示,日粮添加160 mg/kg壳寡糖显著提高回肠粗蛋白质、粗脂肪、灰分、钙和磷的表观消化率(P <0.05),显著提高小肠绒毛高度及绒毛高度与隐窝深度的比值(P <0.05),同时显著提高56 d十二指肠和空肠隐窝细胞增殖活力(P <0.05)。结论:日粮添加160 mg/kg壳寡糖可以通过提高回肠养分表观消化率、绒毛高度和肠上皮细胞的数量来促进消化吸收能力,进而提高断奶仔猪生长性能和健康状态,其作用与盐霉素的效果相当。     

肠出血性大肠杆菌O157:H7研究进展

本文综述了近年来肠出血性大肠杆菌O157:H7的病原学、流行病学、临床诊断及预防控制等方面的研究进展。表明牛是该菌的主要贮存宿主,主要通过食源性途径传播,以患者出现出血性结肠炎、阑尾炎、食管狭窄和结肠穿孔等严重胃肠道并发症为基本特征。目前对该菌的自然携带宿主及其引起的感染尚缺乏有效的治疗手段,因此对该菌的防控就显得尤为重要。     

Escherichia coli in the rumen and colon of slaughter cattle,with particular reference to E. coli O157

The distribution of Escherichia coli O157 and of total E. coli was surveyed in the digestive tract of cattle under 30 months of age, slaughtered between August 1999 and May 2000 in three abattoirs in southern England. Samples were taken from the dorsal and ventral rumen wall, the rumen contents, the colon wall and colon contents, and from faeces or caudal rectal contents. Gut wall samples were processed by vortex-mixer to release loosely adherent bacteria, and by Stomacher to release firmly attached bacteria. E. coli O157 was detected by immunomagnetic separation followed by growth on selective culture media. The numbers of E. coli were higher in the colon than the rumen, and most were located in the digesta phase, rather than associated with the gut wall. The number of E. coli found in the gut and in faeces decreased during the winter months. E. coli O157 was detected more frequently in the colon than in the rumen, but the majority of detections(7/8) were in samples of rumen wall.     

Pre-harvest factors influencing the acid resistance of Escherichia coli and E. coli O157:H7

The effects of pH, acetate, propionate, or butyrate concentration, and diet on acid resistance of fecal Escherichia coli and E. coli O157:H7 were determined by in vitro and in vivo experiments. The pH tested was from 4.0 to 8.0, and the VFA concentrations tested were 0 to 100 mM. The E. coli O157:H7 used was strain 505B. In an in vivo study, cattle were fed a grain-based diet, then either not switched or switched to a grain-based diet with 3% added calcium carbonate or two fiber-based diets (soybean hulls or hay). Acid resistance was expressed as viability after acid-shock at pH 2.0 for 1 h and 4 h for fecal E. coli and E. coli O157:H7, respectively. Enumeration methods used were multitube fermentation, agar plate, and petri-film methods. The E. coli O157:H7 was not found in continuous culture inocula or in vivo samples. The viability of fecal E. coli decreased linearly (P < 0.01) as the culture pH increased, and viability of E. coli O157:H7 was highest (P < 0.01) when cultivated at pH 6.0. The viability of fecal E. coli and E. coli O157:H7 showed quadratic responses (P < 0.05) as acetate and butyrate concentrations increased at pH 7.2, with maximal acid resistance at 20 and 12 mM, respectively. As propionate concentration increased, the acid resistance was not different (P > 0.05) for fecal E. coli. Acid resistance of E. coli was induced by acetate and butyrate, even though the environmental pH was near neutral. Similar results were measured in the in vivo study, where viability after acid shock was more dependent on VFA concentration than on pH. Increasing the dietary calcium carbonate concentration also increased (P < 0.05) acid resistance of fecal E. coli. Results from these studies demonstrated that culture pH and VFA affect acid resistance of E. coli.     

肠道出血性大肠杆菌O157：H7中肠道聚集粘附大肠杆菌耐热肠毒素1基因的检测

应用聚合酶链式反应（Polymerase chaim reaction,PCR）对199株肠道出血性大肠杆菌（enterohemor-rhagic Escherichia coli,EHEC）0157：H7中肠道聚集粘附大肠杆菌耐热肠毒素1（enteroaggregagive Es-cherichia coki heat-stable enteotoxin 1,EAST 1）基因进行了检验。结果，从1％（2／199）菌株中检出了EAST1基因。对其中1株（EHEC0157 96－84）的EAST1基因进行了序列测定。与以往发表的其他致腹泻性大肠杆菌的EAST1基因的序列相比较，EHEC0157 96－84与EAggEC（O42，TL100和160株）、产肠毒素性大肠杆菌（enterotoxigenic E.coli,ETEC）、肠道致病性大肠杆菌（enteropathogenic E.coli,EPEC）、扩散粘附性大肠杆菌（diffusely adherening e.coli,DAEC）的EAST1基因序列相同，但与EAggEC菌株17－2的EAST1基因有1个碱基对不同，从而导致1个氨基酸残 基的变化。本研究结果进一步表明，EAST1或它的变异型基因广泛分仙于致腹泻性大肠杆菌中。     

Farm practices to control E. coli O157 in young cattle--a randomised controlled trial

A randomised controlled trial was used to investigate the effect of three complex management intervention packages to reduce the burden of E. coli O157 in groups of young-stock on cattle farms in England and Wales. All intervention farms were assigned measures to avoid buying in new animals and having direct contact or sharing water sources with other cattle. Furthermore, package A (7 farms) aimed to keep a clean environment and closed groups of young-stock; package B (14 farms) aimed for improved water and feed hygiene, whilst package C was assigned both A and B. The control farms (26 farms) were asked not to alter their practices. Farms, which were assigned intervention package A, exhibited a 48% reduction in E. coli O157 burden over the 4.5 months (average) of observation, compared to 18% on the control farms. The effect of package A compared to the control farms in a crude intention-to-treat model was RR = 0.26 (p=0.122). When the risk ratio was adjusted for actual application of the different measures, the effect of intervention package A became stronger and statistically significant (RR = 0.14 p=0.032). Statistical evidence (p< 0.05) showed that dry bedding and maintaining animals in the same groups were the most important measures within the package and weak evidence (p< 0.1) showed that a closed herd policy and no contact with other cattle may also be of importance. Compliance with the other measures in package A had no influence on the effect of the package. No evidence of effect of the other two intervention packages was found.     

一株O1血清型鸡大肠埃希菌iss基因的序列分析

采用1日龄雏鸡对1株O1血清型鸡源大肠埃希菌(E.coli)的致病性进行测定,并扩增iss基因.结果表明,鸡E.coli O1对1日龄雏鸡具有较强的毒力.iss基因在致病性鸡E.coli O1中的序列与已知禽大肠埃希菌iss基因序列同源性为100%,与人源大肠埃希菌iss基因核苷酸,序列同源性为90.9%,显示了此基因具有保守性.     

Development of intestinal antibodies against Escherichia coli antigens in piglets with experimental neonatal E. coli diarrhoea

Intestinal immune responses to Escherichia coli antigens were studied in conventionally reared piglets orally infected on the first day of life with a virulent enterotoxigenic E. coli (O149: K88). During the first week of life intestinal antibodies were produced against the homologous lipopolysaccharide (LPS) as well as against the K88 antigen and the heat-labile enterotoxin (LT). On Day 7, anti-LPS antibodies of the IgA and IgG classes were detected in most piglets, whereas anti-K88 antibodies of the IgG and IgM classes predominated; antibodies against the enterotoxin were usually of the IgG class. In 21-day-old piglets antibodies of all immunoglobulin classes had usually been produced. In most cases, the levels of intestinal antibodies were substantially higher on Day 21 compared to Day 7, but the levels varied considerably both between and within litters. The intestinal immune responses did not correlate with the severity of clinical symptoms. One-, 7- and 21-day-old piglets reared in a specific-pathogen-free (SPF) herd lacked significant intestinal antibodies to the antigens examined. The oral challenge did not stimulate systemic immune responses. After colostral intake, all piglets had high antibody levels in the circulation. These levels decreased continuously during the 3-week study period. The possibility that high amounts of antibodies in colostrum could interfere with this early intestinal antibody formation should be considered when planning vaccination programmes against E. coli diarrhoea in piglets.     

Occurrence and virulence patterns of E. coli O26, O103, O111 and O145 in slaughter cattle

The study attempted to investigate the occurrence of non-O157 E. coli serogroups O26, O103, O111 and O145 in cattle at slaughter and to determine the virulence potential of these isolates. A total of 399 fecal samples were analyzed by selective plating and E. coli isolates were characterized by polymerase chain reaction (PCR) for the genes vtx1, vtx2, eae and EHEC hlyA. Immunomagnetic separation (IMS) is required to increase the efficiency of the isolation procedure. E. coli O26, O103, O111 and O145 were recovered from 24 (6%) fecal samples. E. coli O26 and O103 seemed to be more abundant in slaughter cattle than E. coli O111 and O145. Sixteen out of the 24 isolates harbored vtx genes. All vtx-positive isolates harbored one or more additional virulence factors. Six out of the 8 vtx-negative isolates harbored eae and/or EHEC hlyA, whereas 2 strains harbored none of the tested virulence genes.     

Escherichia coli O115 forms fewer attaching and effacing lesions in the ovine colon in the presence of E. coli O157:H7

Escherichia coli O115 has been isolated from healthy sheep and was shown to be associated with attaching-effacing (AE) lesions in the large intestine. Following previous observations of interactions between E. coli O157 and O26, the aim of the present study was to assess what influence an O115 AE E. coli (AEEC) would have on E. coli O157 colonisation in vitro and in vivo. We report that E. coli O115- and O157-associated AE lesions were observed on HEp-2 cells and on the mucosa of ligated ovine spiral colon. In single strain inoculum, E. coli O115 associated intimately with HEp-2 cells and the spiral colon in greater numbers than E. coli O157:H7. However, in mixed inoculum studies, the number of E. coli O115 AE lesions was significantly reduced suggesting negative interference by E. coli O157. Use of the ligated colon model in the present work has allowed in vitro observations to be extended and confirmed whilst using a minimum of experimental animals. The findings support a hypothesis that some AEEC can inhibit adhesion of other AEEC in vivo. The mechanisms involved may prove to be of utility in the control of AE pathovars.