Effect of Nutrition on In Vitro Biofilm Formation of Gastrointestinal Associated Microbes

Abstract

Gastrointestinal (GI) health is an important contributor to one’s overall well-being. In the past decade, the focus of this aspect of health has been on the organisms that inhabit the intestines: gut microbes. A concept central to understanding bacterial behavior for health or disease promotion is biological film (biofilm) formation. The predominant form of growth for bacteria is biofilm formation, an as yet poorly described phenomenon for gut microbes. In order to better understand bacterial behavior in response to nutrients that pass through the GI system, a high throughput system to assess biofilm formation was developed. Gastrointestinal-associated microbes, Escherichia coli and Enterococcus faecalis, were assayed for biofilm formation in 96-well plates after 24 hours of incubation. Nutrients, inter-and intrakingdom signaling molecules such as monosaccharides, calcium, insulin, endocannabinoids, and AI-1, AI-2 like signaling compounds, respectively, were added to cultures in order to test their effects on biofilm formation. Biofilm was quantified spectrophotometrically by the measurement of optical density of each well measured at 580nm following crystal violet staining of adherent biofilm. Values were expressed as means ± standard error of the mean (SEM); differences between means were assessed using t-testing and ANOVA using GraphPad Prism, with mean differences considered significant at P < 0.05.

Results showed that biofilm formation by E. coli was enhanced by glucose, galactose, lactose, AI-1 like signaling compound and insulin at 50 and 100µU/ml, while AI-2 like compound and calcium inhibited biofilm formation. Biofilm formation by E. faecalis was also enhanced by AI-1 like compound and insulin at 50µU/ml in RPMI medium and inhibited in cultures grown in BHI medium or with added calcium. We conclude that gastrointestinal-associated microbes are influenced by nutrients as well as various factors, including the culture medium, signaling compounds, as well as host-signaling compounds such as insulin and calcium. This study provides a platform required for future studies involving nutrient effect on biofilm formation.