Biofilm-producing Escherichia coli O104:H4 overcomes bile salts toxicity by expressing virulence and resistance proteins.

This article focuses on the effects of bile salts on biofilm formation, protein expression, and epithelial cell adherence in pathogenic Escherichia coli strains, particularly those of the O104:H4 serotype carrying the Shiga toxin gene (stx2a). Among 82 strains tested, only two isolates from a 2009 outbreak in the Republic of Georgia demonstrated strong or moderate biofilm formation in the presence of bile salts and expressed proteins linked to multidrug resistance and stress response, including OmpC, F0F1 ATP synthase, H-NS, and L7/L12. These strains also showed high adherence to human intestinal Caco-2 epithelial cells, although adherence was generally reduced when bile salts were present during infection assays. The findings suggest that bile salts induce phenotypic changes that may enhance the survival and virulence of E. coli O104:H4 in the host environment.