Understanding the early pathogenesis and virulence of necrotic enteritis in broiler chickens

越来越大的消费者压力迫使畜牧业开发替代品，或者至少大幅减少抗生素的使用量。我们必须找到有效的工具来预防坏死性肠炎(NE)，这是一种影响不含抗生素的鸡的致命疾病。肺炎肺炎是由A型产气荚膜梭菌引起的，但诱因是必要的，以创造有利于产气荚膜梭菌(CP)菌株数量增加的肠道环境。毒素netB的存在被认为是致病性所必需的。疾病过程的另一部分被认为依赖于引起NE的菌株取代鸡肠道中非致病性共生菌株的能力。许多革兰氏阳性细菌已被证明能产生各种称为细菌素的蛋白质类有毒化合物，并抑制密切相关菌株的生长。Perfrin是一种染色体编码的细菌素，已在致病的NetB阳性NE致病菌株中被发现，并被认为发挥了重要作用。在琼脂斑点试验上检测各种CP菌株时，我们观察到并不是所有netB阳性的CP菌株都携带Perfrin基因，而是产生了Perfrin以外的细菌素，并且一些共生CP菌株可以抑制致病CP菌株的生长。*我们建立了一种复制鸡坏死性肠炎的体内结扎肠环模型，并注意到病变的严重程度与肠道绒毛内CP细菌的数量有关(Parent等，2016)。因此，CP与肠细胞的黏附可能在NE的发病机制中发挥作用，因此我们对IV型菌毛蛋白感兴趣，它被认为在黏附细胞表面方面发挥作用。所有这些最新的发现，都导致了这一建议研究计划的发展。这项拟议的工作是创新的，使用一个独特的CP菌种库，可以访问新的动物模型(结扎肠环模型)，以培训快速发展的基因组学、转录学和生物信息学领域的高素质人员。它将提供独特的答案，并为一个伦理问题带来新的解决方案，即使用抗生素养鸡。这一建议代表了我在过去几年进行的关于进一步了解坏死性肠炎的研究计划的合乎逻辑的连续性。*我的研究计划的目的是更好地了解NE早期感染步骤背后的致病机制，更准确地说，1)鉴定和表征新的CP细菌素，2)验证不同IV型菌毛蛋白基因的免疫原性，3)使用我们的结扎肠环模型，利用免疫组织化学、生物标记和细菌转录转录技术，识别参与早期发病的基因及其对宿主的影响。这一认识对于长期目标是关键，这些目标是开发有效和有针对性的NE预防工具，如益生菌和疫苗。

An increasing consumer pressure is forcing animal agriculture to develop alternatives, or at least to substantially reduce the amount of antibiotics used. We must find effective tools to prevent necrotic enteritis (NE), a deadly disease from affecting antibiotic-free chickens. NE is caused by Clostridium perfringens type A, but predisposing factors are necessary to create an intestinal environment conducive to the increase in number of C. perfringens (Cp) strains. The presence of the toxin netB is thought to be essential for pathogenicity. Another part of the disease process is thought to rely on the ability of NE-causing strains to displace non-pathogenic commensal isolates from the gut of chickens. Numerous Gram positive bacteria have been shown to produce various proteinaceious toxic compounds called bacteriocins, and inhibiting the growth of closely related strains. Perfrin, a chromosomally-encoded bacteriocin has been identified in pathogenic netB positive NE-causing strains and thought to play an important role. When testing various Cp strains on agar spot test, we observed that not all netB positive Cp strains carry the perfrin gene, that bacteriocins other than perfrin were produced, and that some commensal Cp strains can inhibit the growth of pathogenic Cp strains.******We have developed an in vivo ligated intestinal loop model reproducing necrotic enteritis in chickens and noted that lesion severity was correlated with numbers of Cp bacteria lining the intestinal villi (Parent et al, 2016). Thus, Cp adherence to the enterocyte might play a role in the pathogenesis of NE hence our interest in type IV pilins which are known to play a role in adherence to cell surface. All of these recent findings, have led to the development of this suggested research program. The proposed work is innovative, using a unique Cp strains bank with access to a new animal model (ligated intestinal loop model) to train highly qualified personal in the rapidly developing field of genomics, transcriptomics and bioinformatics. It will provide unique answers and bring new solutions to an ethical problem, which is the use of antibiotics to grow chickens. This proposal represents a logical continuity of the research program on further understanding necrotic enteritis I have conducted in the past years. ******The objectives of my research program are to better understand the pathogenic mechanisms underlying the early infection steps of NE, more precisely 1) identify and characterize new Cp bacteriocins, 2) verify the immunogenicity of different type IV pilin genes, 3) use our ligated intestinal loop model to identify genes involved in early pathogenesis and their effects on the host, using immunohistochemistry, biological markers and bacterial transcriptomics. This understanding is key to long-term objectives which are the development of efficacious and targeted NE preventive tools such as probiotics and vaccines.*****