Bile acids stimulate biofilm formation in Vibrio cholerae

Abstract

SummaryVibrio cholerae is a Gram-negative bacterium that causes the acute diarrhoeal disease cholera. After the bacterium is ingested, it passes through the digestive tract, encountering various environmental stresses including the acidic milieu of the stomach and the toxic effects of bile in the duodenum. While these stresses serve as part of a host defence system, V. cholerae has evolved resistance mechanisms that allow it to evade these defences and establish infection. We examined the expression profiles of V. cholerae in response to bile or bile acids and found an induction of biofilm genes. We found that V. cholerae shows significantly enhanced biofilm formation in response to bile acids, and that bacteria within the biofilm are more resistant to the toxicity of bile acids compared with planktonic cells. Bile acid induction of biofilms was found to be dependent on the vps genes ( Vibrio polysaccharide synthesis) and their transcriptional activator VpsR, but VpsT is not required. These results contribute to the developing picture of a complex relationship between V. cholerae and its environment within the host during infection.

Signals, Regulatory Networks, and Materials That Build and Break Bacterial Biofilms

“…For example, bile acids, which are detergents secreted into the small intestine through the bile duct, normally kill bacteria by solubilizing the bacterial cell membrane (22). V. cholerae, a diarrheal pathogen which is thought to colonize the small intestine, increases biofilm formation in response to bile acids (137). These results suggest that bile can actually have a protective effect on V. cholerae passing through the digestive system of the host by promoting biofilm formation.…”

The Bile Response Repressor BreR Regulates Expression of the Vibrio cholerae breAB Efflux System Operon

“…1). Since the effect of bile on V. cholerae has been determined previously using 0.4% crude bile (15,21,22,48), a concentration within the estimated range of concentrations of individual bile salts in the intestine (0.2 to 2%) (20), we utilized this concentration as the high bile concentration, whereas 0.02% crude bile was employed as the low bile concentration because it was 10-fold lower than the lowest individual bile salt concentration in the intestine (0.2%) (20). Samples were obtained at 2, 4, and 5.5 h from the high-bile cultures and at 2 h from the low-bile cultures (Fig.…”

“…However, the ompT mRNA level in the presence of the high bile concentration was decreased 24-fold compared to the baseline level at the 5.5-h time point, and this trend was reverted in the presence of the low bile concentration, although we did not detect changes in ompU mRNA levels at any of the different time points. None of the genes involved in biofilm formation in the presence of bile (vps genes and vpsR) (22) were identified using our criteria. This outcome was anticipated, though, since our experimental conditions did not promote biofilm formation.…”

“…This pathogen has developed several mechanisms to mediate protection against the action of bile: (i) it increases motility in the presence of bile, which is hypothesized to be important for the bacterium to swim away from high concentrations of bile in the lumen, penetrate the mucus layer, and gain access to the underlying epithelial cells for colonization (15,48) (see Fig. 1A); (ii) it induces the formation of a biofilm, in which the cells are more resistant than nonbiofilm cells to the bactericidal effect of bile (22); (iii) it enhances the expression of ompU (encoding a small-pore porin) and decreases the expression of ompT (encoding a large-pore porin), reducing bile uptake (4,43,44); and (iv) it induces the expression of genes that encode proteins involved in efflux, such as AcrA (7) and TolC (3), and efflux pumps, such as VceB (8), VexB, and VexD (4).…”

Sugar source modulates exopolysaccharide biosynthesis in Bifidobacterium longum subsp. longum CRC 002

“…In Bifidobacterium animalis subsp. lactis, EPS production seems to be enhanced in the presence of bile (RuasMadiedo et al, 2009), as has been found for two pathogenic Vibrio species (Hsieh et al, 2003;Hung et al, 2006). Surface polysaccharides are well known as virulence and colonization factors of pathogenic bacteria, but molecules produced by commensal gut micro-organisms are gaining attention for their role in developing a normal immune system through communication with the mammalian host (reviewed by Mazmanian & Kasper, 2006).…”