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

新出现的多重耐药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传播到食物链。替代的抗微生物化合物被越来越多地使用，如短链脂肪酸(SCFA)，它通常存在于结肠中，但具有抗微生物特性。过去40年来，特别是在西方世界，超临界脂肪酸的生产和使用大幅增加，其中一种超临界脂肪酸--丙酸(PA)的产量现在每年价值约12亿GB，而且还在增加。PA的有效性和低成本使农民能够在减少抗生素使用的同时处理谷物和动物饲料，导致PA被建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，通过添加饲料和水，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也被证明是非常受欢迎的，因为它对人类无毒，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物中，总重量最高可达食物的1%。西方饮食现在含有越来越多的食品添加剂，这些添加剂的添加在延长食品保质期和减少食源性疾病的同时，也与令人担忧的致衰性肠道疾病的流行增加不谋而合。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而加剧，如肠道中的细菌。到目前为止，将这些遗传、饮食和微生物因素联系在一起的确切解释被证明是难以捉摸的。在这项提案中，我们将展示PA正在促进家禽中暴露于PA的致病性大肠杆菌转移到人体肠道中富含PA的环境中。粘附性和侵袭性大肠杆菌(AIEC)一直是从CD患者的肠道中分离出来的。这些细菌的不同寻常之处在于，它们没有毒素或其他使它们有别于病原体的因素。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，这有时会导致AIEC的行为发生显着变化。PA引起的这些变化包括肠道细胞入侵增加，在这些细胞内持续存在，以及形成称为生物膜的结构的能力，使细菌能够在更高浓度和更长时间内耐受抗生素。当从农业的角度看实验室对PA的这种适应时，可以看到，如果AIEC在环境中遇到PA，它会准备或使它们适应人类肠道，那里PA水平很高，对大多数病原体都有限制，特别是在下肠或结肠。然而，AIEC会在整个人类肠道内建立感染，即使在沙门氏菌和弯曲杆菌不能感染的地方也是如此。因此，AIEC似乎很好地适应了PA，提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被认为与禽类致病性大肠杆菌(APEC)有关，这种病原体在鸡等禽类中发现。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有惊人的相似之处。这项提案将寻求确定家禽业和其他地方使用PA的高水平是否有助于病原体的进化，这些病原体现在能够导致人类肠道疾病。这项提案将首次显示克罗恩病、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剂。

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.