In vitro, ex vivo and in vivo effects of egg consumption (and egg microbiota) on the microbial community composition of gut microbiota and on immunological/metabolic/inflammatory biomarkers

Abstract

Background and Objectives: Some years ago, egg consumption was considered to be bad for heart health, blood vessels or for people watching their cholesterol levels. Meanwhile, recent meta-analysis studies concluded that higher consumption of egg is not associated with increased risk of cardiovascular disease. This discrepancy raises an important question as to whether the gut microbiota plays a role in digestion, absorption and metabolism of eggs in the digestive tract. There are four primary ways in which eggs (or egg consumption) can impact on the composition of the intestinal microbiota: a) by its nutrition-related factors; through its microbiological status; b) through the potential presence of residues of drugs applied to laying hens; and d) through its allergens. Current studies suggest that high dietary fat intake may contribute to metabolic syndrome pathogenesis through altering intestinal microbiota (a decrease in gut barrier-protecting beneficial Bifidobacteria spp. population and an increase in E coli population), increasing intestinal permeability, and promoting inflammation [Brown et al., 2012; Martinez-Medina et al., 2014]. Because per capita consumption of egg has increased continuously (221 – 259 eggs) and eggs contain high levels of cholesterol and saturated-fat, we were interested in investigating whether egg consumption and egg microbiota impact on the composition of the gut microbiota and immunological/metabolic/inflammatory biomarkers in vitro, ex vivo and in vivo. Materials and Methods: Briefly, freshly defecated fecal pellets were collected aseptically from 6 – 8 donor mice, weighed, and then placed in 200 ml of MRS broth. The fecal pellets were resuspended in 200 ml MRS broth by vortexing and by gently bashing with a sterile bacteriological loop, and the resulting cell suspensions were incubated anaerobically without or with whole boiled eggs at 37 °C for 24h. After incubation, serial dilutions were made in sterile PBS and suitable dilutions were plated onto MRS agar for anaerobic culturable bacteria. Afterwards, MRS agar plates were incubated anaerobically at 37 °C for 48 hours and the numbers of colonies on the plates were counted. After the plating process, bacterial cultures were used to measure pH values. For the first time, we used Konelab 20i Clinical Chemistry Analyzer to assess the actual rate of glucose consumption by bacteria, as manifested by quantitative measurement of glucose concentrations in bacterial cell-free culture supernatants (showing the rate of glucose disappearance). However, we conducted similar experimental series with a pure culture of the human-derived Bifidobacterium DSM 20086 strain. Results: Our preliminary in vitro and ex vivo experiments show that addition of egg to MRS broth medium did not inhibit, but rather augmented the growth of culturable anaerobic bacteria from mouse faeces as well as human intestinal-derived Bifidobacterium DSM 20086 strain, as manifested by higher bacterial counts (CFU/ml). This was associated with lower pH values and glucose concentrations in bacterial cultures as reliable and quantitative indicators for prediction of the rate of glucose utilization. Conclusion: Overall, our experiments show that although egg contains high cholesterol and saturated-fat contents, it has not any demonstrably negative impacts on bacterial growth parameters in culturable anaerobic bacteria from mouse faeces as well as human-derived Bifidobacterium DSM 20086 strain. If this happens in vivo, then egg consumption may beneficially modify gut microbiota community composition, which in turn may play a favorable role in the digestion, absorption and metabolism of egg in the digestive tract. Our ongoing cell culture and in vivo studies will provide additional insights into the molecular and cellular basis, underpinning the interplay between egg metabolism and gut microbiota composition.