Effects of Nutritional Fat on the Growth of Intestinal E. Coli

Infectious diarrhea causes substantial morbidity in Western countries and the developing world and leads to the use of considerable health resources. Antibiotic resistance continues to increase, potentially leading to a decrease in therapeutic options in the future. Important pathogens include Salmonella typhimurium (S. typhimurium) and pathogenic Escherichia coli (E. coli) which are genetically closely related.

The human intestine has considerable colonization resistance against bacterial pathogens. This resistance is largely mediated by the gut microbiota. Therefore, previous exposure to antibiotics or immunosuppression leading to a breakdown of the intestinal defense systems increase the risk for subsequent infection with S. typhimurium.

The composition of the human microbiome undergoes dramatic changes upon exposure to various factors including nutrition, physical activity, drugs and much more. Most studies focused on long-term exposure to various factors; however, since bacterial growth is rapid (doubling time of S. typhimurium under optimal conditions = 20min), even short-term variations in the environment could dramatically influence the human microbiota.

In the lab of Prof. WD Hardt, a mouse model of S. typhimurium enterocolitis has been established. Since most mouse strains are resistant against colonization with S. typhimurium, pretreatment with antibiotics is a requirement for induction of S. typhimurium enterolitis. However, recent experiments in the Hardt lab revealed, that in mice, 24 h exposure to a high-fat diet also results in a breakdown of colonization resistance, leading to Salmonella enterocolitis upon S. typhimurium infection. The same is true for E. coli strains. Subsequent experiments demonstrated that exposure to fatty acids is sufficient to overcome colonization resistance. Mechanistic experiments identified fat-elicited bile-release as the underlying mechanism: Exposure to a high fat diet leads to increased bile acid secretion; S. typhimurium can tolerate 10-fold higher bile acid concentrations than commensal bacterial, leading to a growth advantage of S. typhimurium compared to competing bacteria (WD Hardt et al., unpublished data).

The aim of this study is to verify the results of this study in human healthy volunteers. The nutritional habits of all participants will be carefully evaluated. In the intervention phase, participants will be exposed to either high-fat or low-fat diet and a controlled dose of the non-pathogenic bacteria E. coli Nissle. E. coli Nissle is the active compound for "Mutaflor®" and other probiotics. E. coli Nissle has therapeutic effects for the treatment of chronic inflammatory intestinal diseases. In contrast to other non-pathogenic E. coli strains, it exhibits a specific pattern of fitness factors but lacks prominent virulence factors. In vivo and in vitro experiments demonstrated both, protective effects against infection with intestinal pathogens as well as potent immunomodulatory properties. Growth of E. coli Nissle in the human gut resembles growth of S. typhimurium. Both bacteriae also share metabolic requirements for intestinal growth. Therefore, growth E. coli Nissle in the human intestine can be used as a marker for growth of E. coli strains, Salmonella typhimurium and related pathogens.