Propionic acid use in agriculture and food production is driving evolution of novel Escherichia coli pathotypes

新出现的耐多药细菌菌株迫使农业和食品生产行业重新考虑使用抗生素，以防止食品变质和病原体进入食物链。替代抗微生物化合物越来越多地被使用，如短链脂肪酸（SCFA），通常在结肠中发现，但具有抗微生物特性。在过去的40年里，SCFA的生产和使用大大增加，特别是在西方世界，其中一种SCFA，丙酸（PA）的生产现在每年价值约12亿英镑，而且还在上升。PA的功效和低成本使农民能够在处理谷物和动物饲料的同时减少抗生素的使用，因此PA被提议作为发展中国家抗生素过度使用的解决方案。PA已被证明在家禽生产中非常成功，通过饲料和水的添加，它减少了沙门氏菌和弯曲杆菌的携带，这是英国食源性疾病的常见原因。PA也被证明非常受欢迎，因为它对人体无毒，几乎没有副作用。因此，PA可以添加到包括蛋糕、面包和蜜饯在内的食品中，最多占食品总重量的1%。如今，西方饮食中食品添加剂的含量越来越高，它们的添加在延长食品保质期、减少食源性疾病的同时，也伴随着令人担忧的肠道疾病患病率的上升。炎症性肠病，如克罗恩病（CD）和溃疡性结肠炎（UC），虽然与潜在的遗传条件有关，但会因饮食和其他因素（如肠道中的细菌）而加剧。迄今为止，将这些遗传、饮食和微生物因素联系在一起的明确解释一直难以捉摸。在本提案中，我们将证明PA正在促进暴露于家禽中PA的致病性大肠杆菌转移到富含PA的人类肠道环境中。粘附性和侵袭性大肠杆菌（AIEC）一直从乳糜泻患者的肠道中分离出来。这些细菌是不寻常的，因为它们没有毒素或其他因素，将它们区分为病原体。然而，与大多数其他细菌不同，AIEC可以在防腐剂PA上生长和存活，这及时引起AIEC行为的显着变化。这些PA诱导的变化包括增加对肠道细胞的侵袭，在这些细胞内持续存在，以及形成一种称为生物膜的结构的能力，这种结构使细菌能够在更高浓度和更长时间内抵抗抗生素。当从农业的角度看待实验室中对PA的适应时，可以看出，如果AIEC在环境中遇到PA，它将使它们适应或适应人类肠道，因为PA水平很高，对大多数病原体具有限制性，特别是在下肠或结肠中。然而，AIEC在整个人体肠道内建立感染，甚至在沙门氏菌和弯曲杆菌无法感染的地方。因此，AIEC似乎很好地适应了PA，这就引出了这种适应是如何以及在哪里发生的问题。值得注意的是，AIEC被认为与一种叫做禽致病性大肠杆菌（APEC）的病原体有关，这种病原体存在于鸡等禽类中。这些APECs越来越被认为是人类疾病的病原体，从全身感染中分离出的大肠杆菌，包括尿路和脑膜炎，与APECs有着惊人的相似之处。该提案将寻求确定家禽业和其他地方的高水平PA使用是否有助于病原体的进化，这些病原体现在能够在人体肠道中引起疾病。这一建议将首次表明克罗恩病、西方饮食和AIEC之间的明确联系，并确定丙酸是推动这种关系的促进者。

Emerging multidrug resistant strains of bacteria have forced both the agricultural and food production industries to rethink the use of antibiotics as a means of preventing both food spoilage and transmission of pathogens into the food chain. Alternative anti-microbial compounds are increasingly used such as short chain fatty acids (SCFA), commonly found in the colon but with anti-microbial properties. SCFA production and use has increased greatly in the past 40 years, particularly in the Western world, with the production of one such SCFA, propionic acid (PA), now worth approximately £1.2 billion per year and rising. PA efficacy and low cost allows farmers to treat grain and animal feed while reducing antibiotic use, resulting in PA being proposed as a solution in developing countries to antibiotic overuse. PA has proven highly successful in poultry production where through feed and water addition it has reduced carriage of Salmonella and Campylobacter, common causes of food borne sickness in the UK. PA has also proved highly popular as it is non-toxic to humans with few, if any, side effects. PA therefore can be added to foodstuffs including cakes, bread and preserves at up to 1% total weight of the food. The Western diet now contains increasing levels of food additives whose addition while prolonging the shelf life of food and reducing food borne disease, has also coincided with worrying increases in the prevalence of debilitating gut diseases. Inflammatory bowel diseases such as Crohn's Disease (CD) and ulcerative colitis (UC) while linked to underlying genetic conditions are exacerbated by dietary and other factors, such as bacteria in the intestine. A definitive explanation to link these genetic, dietary and microbial factors together has to date proved elusive. In this proposal we will show that PA is facilitating the transfer of pathogenic E. coli that are exposed to PA in poultry, to the PA rich environment of the human intestine. Adherent and invasive E. coli (AIEC) are consistently isolated from the intestine of CD sufferers. These bacteria are unusual in that they lack toxins or other factors that would set them apart as pathogens. However unlike most other bacteria AIEC can grow and survive on the preservative PA which in time induces significant changes in the behaviour of AIEC. These PA induced changes include increased invasion of cells of the intestine, persistence within these cells and an ability to form structures called biofilms that enable the bacteria to resist antibiotics at higher concentrations and for longer. When this adaptation to PA in the lab is looked at from an agricultural perspective it can be seen that if AIEC were to encounter PA in the environment it would prepare or adapt them to the human intestine where levels of PA are high and restrictive for most pathogens, particular in the lower intestine or colon. However, AIEC establish infection throughout the human intestine, even in places where Salmonella and Campylobacter cannot. AIEC therefore appear well adapted to PA begging the question of how and where this adaptation occurred. Significantly AIEC are thought to be related to pathogens called avian pathogenic E. coli (APEC) that are found in birds such as chickens. These APECs are increasingly being recognized as causative agents of human disease with E. coli isolated from infections throughout the body, including the urinary tract and meningitis, bearing striking similarities to APECs. This proposal will seek to establish if high levels of PA use in the poultry industry and elsewhere is contributing to the evolution of pathogens that are now capable of causing disease in the human intestine. This proposal will for the first time show a definitive link between Crohn's Disease, the Western diet and AIEC, and identify propionic acid as being a facilitator in driving this relationship.