Bile salts enhance bacterial co-aggregation, bacterial-intestinal epithelial cell adhesion, biofilm formation and antimicrobial resistance of Bacteroides fragilis

Microb Pathog. Aug-Sep 2007;43(2-3):78-87. doi: 10.1016/j.micpath.2007.04.002. Epub 2007 Apr 20.


Bacteroides fragilis is the most common anaerobic bacterium isolated from human intestinal tract infections. Before B. fragilis interacts with the intestinal epithelial cells, it is exposed to bile salts at physiological concentrations of 0.1-1.3%. The aim of this study was to determine how pre-treatment with bile salts affected B. fragilis cells and their interaction with intestinal epithelial cells. B. fragilis NCTC9343 was treated with conjugated bile salts (BSC) or non-conjugated bile salts (BSM). Cellular ultrastructure was assessed by electron microscopy, gene expression was quantified by comparative quantitative real-time RT-PCR. Adhesion to the HT-29 human intestinal cell line and to PVC microtitre plates (biofilm formation) was determined. Exposure to 0.15% BSC or BSM resulted in overproduction of fimbria-like appendages and outer membrane vesicles, and increased expression of genes encoding RND-type efflux pumps and the major outer membrane protein, OmpA. Bile salt-treated bacteria had increased resistance to structurally unrelated antimicrobial agents and showed a significant increase in bacterial co-aggregation, adhesion to intestinal epithelial cells and biofilm formation. These data suggest that bile salts could enhance intestinal colonization by B. fragilis via several mechanisms, and could therefore be significant to host-pathogen interactions.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Bacterial Adhesion / drug effects*
  • Bacteroides fragilis / drug effects*
  • Bacteroides fragilis / genetics
  • Bacteroides fragilis / ultrastructure
  • Bile Acids and Salts / pharmacology*
  • Biofilms / drug effects*
  • Biofilms / growth & development
  • Cell Line
  • Drug Resistance, Bacterial
  • Epithelial Cells / microbiology
  • Gene Expression Profiling
  • Gene Expression Regulation, Bacterial
  • Humans
  • Intestines / cytology
  • Intestines / microbiology*
  • Microbial Viability
  • Microscopy, Electron, Scanning
  • Microscopy, Electron, Transmission
  • RNA, Bacterial / biosynthesis
  • RNA, Messenger / biosynthesis
  • Reverse Transcriptase Polymerase Chain Reaction


  • Anti-Bacterial Agents
  • Bile Acids and Salts
  • RNA, Bacterial
  • RNA, Messenger