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

点击翻译按钮获取中文摘要

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.