Cloning and Sequencing of cnf1 from Escherichia coli Incriminated in Mink and Bovine Colibacillosis

Colibacillosis is responsible for significant losses to the mink and cattle industries. Previous work in our laboratory and by others has suggested that possession of cnf1, the gene encoding cytotoxic necrotizing factor (CNF1), may contribute to the virulence of isolates of E. coli from mink and cattle. The cnf1 gene from E. coli isolated from a mink with colisepticaemia and a bovid with scours was amplified and cloned as a 3.5 kb fragment, and the fragment was sequenced. The cnf1 sequences from the mink and bovine isolates of E. coli were compared to each other and to cnf1 sequences of E. coli from urinary tract and diarrhoea-associated infections of humans. The difference was only 7 nucleotides between the cnf1 sequences of the mink and bovine isolates of E. coli, which translated into 7 differences in amino acids. The cnf1 sequence of the mink isolate of E. coli had 15 nucleotide differences from the cnf1 sequences of the human isolate of E. coli (GenBank X70670), which translated into 11 differences in amino acids between these proteins. The cnf1 sequence of the bovine isolate of E. coli had 14 nucleotide differences from the cnf1 sequence of the human isolate of E. coli (GenBank X70670), which translated into 10 differences in amino acids between these proteins. The highly conserved sequences of the amino acids of CNF1 proteins make them a promising target for detection and control of the CNF1-producing E. coli involved in disease among various host species.     

仔猪黄痢、白痢病原调查报告

对深圳某猪场，通过实验室手段进行仔猪黄痢、白痢病原调查，结果显示：除含有致病性大肠杆菌Ｋ＿（８８）．（３４．３％）外，尚含有Ｋ＿（９９）（８．６％）、Ｆ＿（４１）（２７．３％）．以及轮状病毒（４０％），同时还分离出一株等孢子球虫，证实本地区仔猪黄痢、白痢病原复杂。     

Resistance to Serum Complement,iss, and Virulence of Avian Escherichia coli

Control of avian colibacillosis is hampered by lack of easily identifiable markers for virulent Escherichia coli. Resistance to serum complement appears to be a widespread trait of virulent avian E. coli, suggesting that bacterial factors promoting survival in serum may be useful in discriminating between virulent and avirulent isolates. Such distinguishing factors may prove useful in diagnostic protocols or as targets in future colibacillosis control protocols. Interestingly, the factors responsible for resistance to complement differ in the E. coli isolated from mammalian and avian hosts, which may reflect differences in the nature of avian and mammalian colibacillosis. In some cases, genetic determinants for serum complement resistance in avian E. coli are found on aerobactin- or Colicin V-encoding plasmids. One such gene, iss, first described for its role in the serum resistance associated with a ColV plasmid from a human E. coli isolate, occurs much more frequently in isolates from birds with colibacillosis than in faecal isolates from healthy birds. Efforts to identify the genomic location of iss in a single, virulent avian E. coli isolate have revealed that it occurs in association with several purported virulence genes, all linked to a large conjugative R plasmid. At this time, it is not known whether iss merely marks the presence of a larger pathogenicity unit or is itself a contributor to virulence. Nevertheless, the presence of the complement-resistance determinant, iss, may be a marker of virulent avian E. coli exploitable in controlling avian colibacillosis.     

37℃热应激对实验性大肠杆菌病肉鸡肺动脉压和右心功能的影响

160只商品代AA肉仔鸡于29日龄时随机均分为常温对照组、热应激对照组、常温感染组和热应激感染组．研究了37℃热应激对实验性感染大肠杆菌肉鸡肺动脉压和右心功能的影响。结果37℃热应激1～3d极显著降低（P〈0．01）肉鸡感染大肠杆菌引起的肺动脉高压，肺动脉收缩压、舒张压和平均肺动脉压分别下降了34．78％、45．83％、40．48％。热应激3、7d，感染大肠杆菌肉鸡右心室收缩压显著下降（P〈0．05，P〈0．01），分别下降了26．60％、28．00％，右心室收缩和舒张压最大变化速率显著下降（P〈0．05），分别下降了77．50％，50．77％和75．00％、50．58％。结果表明，37℃热应激可以拮抗肉鸡感染大肠杆菌引起的肺动脉高压，降低感染肉鸡死亡率，但使右心功能下降。     

Effect of weaning age, protein nutrition and enterotoxigenic Escherichia coli challenge on the health of newly weaned piglets

The objective of this experiment was to determine whether decreasing dietary protein content and increasing weaning age could improve piglet health and decrease the occurrence and severity of post-weaning colibacillosis (PWC) in the absence of in-feed antimicrobial growth promoters (AGPs). The experiment consisted of a 2 × 2 × 2 factorial combination of weaning age (4 vs 6 weeks), dietary protein content (H vs L; 230 vs 130 g CP/kg) and experimental enterotoxigenic Escherichia coli (ETEC) challenge (+ vs −). On day 3 post-weaning half of the piglets were challenged per os with 10⁹ cfu ETEC. A sample of piglets was euthanased on days 0 and 6 to assess digesta pH and lactobacilli to coliform (L:C) ratio. ETEC excretion persisted longer in the 4-week-weaned piglets than those weaned at 6 weeks (P = 0.003), and the numbers of ETEC shed tended to be higher on the H than L diet, especially in the 4-week-weaned piglets (P = 0.093). Decreasing protein level led to significantly firmer faeces, decreased pH and increased L:C ratio of proximal colon digesta. These results suggest that in the absence of AGPs, increasing weaning age and decreasing dietary protein level, especially in earlier weaned piglets, may help to minimize the effects of PWC.     

Effects of sub-clinical post-weaning colibacillosis and dietary protein on acute phase proteins in weaner pigs

There is an increasing body of evidence that plasma acute phase proteins (APP) can be used as a marker to assess pig health. The objective of this study was to assess whether experimentally induced sub-clinical post-weaning colibacillosis (PWC) affects the concentration of two plasma APP, i.e. haptoglobin (Hp) and C-reactive protein (CRP). Since sub-clinical PWC is sensitive to protein supply, we additionally assessed whether these APP responses are sensitive to dietary protein contents. Weaned pigs (6 groups of 9 each) were offered one of the three foods, i.e. H (230 g CP/kg), L (130 g CP/kg) or HA (23% CP with anti-microbial growth promoters). On day 5 post-weaning, pigs were either dosed with 10⁸ colony forming units of enterotoxigenic E. coli or were sham-infected. Three days later and across feeding treatments, infection had reduced feed intake. Feeding and infection treatment significantly interacted for both Hp and CRP. Infection increased Hp concentration in H and HA pigs, but not in L pigs, whilst infection increased CRP concentration to a larger extent in HA pigs than in H and L pigs. The results suggest that sub-clinical PWC leads to changes in APP profiles and that these changes may be sensitive to dietary protein contents. Usefulness of APP to describe health status in pigs may therefore need to be considered in relation to their nutritional environment.     

家蝇抗菌肽提取及对鸡大肠杆菌病药效试验

体外抑菌试验结果证明抗菌肽对O1型血清大肠杆菌的药敏抑菌圈直径为19.3±0.32mm,以O1型大肠杆菌感染14日龄岭南黄肉用雏鸡,24 h后分别用抗菌肽高、中、低剂量及环丙沙星混饮给药,以比较其疗效。通过临床观察、尸体解剖、细菌检验结果表明,试验药物组与感染对照组差异极显著(P<0.01),即试验药物对鸡大肠杆菌病有良好疗效;抗菌肽高、中剂量与环丙沙星疗效相当(P>0.05),且不影响鸡只的正常增重(P>0.05)。     

仔猪大肠杆菌病病原菌分离鉴定与初步防治

从河南１２个发病场采得４４份仔猪黄、白痢检样，共分离出大肠杆菌３６株，经血清学试验鉴定为Ｏ１３９８株，Ｏ１０１７株，Ｏ１３８７株，Ｏ４５３株，Ｏ６０３株，Ｏ１４１２株，Ｏ１４７１株，Ｏ８１株，另有４株未能定型。对不同分离株进行了药敏试验。利用所分离菌株研制出灭活铝胶菌苗注射产前母猪，其后代黄、白痢发病率大大降低。     

猪大肠杆菌病的临床表现及危害性

猪大肠杆菌病是由病原性大肠杆菌引起的以初生仔猪和断奶仔猪为主的肠道感染性传染病。由于其发病率和死亡率高,易发生耐药性,给本病的防控带来了一定困难。文章着重对猪大肠杆菌病临床类型及对应的症状、病理变化和危害性进行介绍,为防控本病提供参考。     

鸡新城疫与大肠杆菌病混合感染的诊治

鸡新城疫是由鸡新城疫病毒引起的一种急性、高度接触性传染病,致死率较高。目前,我国普遍采用以新城疫疫苗接种为主的综合防控措施,能够在很大程度上控制该病的大规模流行。鸡大肠杆菌病是由大肠埃希菌感染引起的传染病,多个血清型的大肠埃希菌是多种动物肠道内的常驻菌,因此其分布极为广泛,致病率也较高,并且多与其他疫病混合感染。通过开展病死鸡的病理变化检查、实验室检验以及分离菌株的药物敏感性试验,对临床接诊的鸡新城疫及大肠杆菌混合感染病例进行诊断并提出综合防控措施,以期为兽医临床2种疾病的防控提供有益参考。