Final answer:
The production of indole by E. coli encourages the tightening of tight junctions and enhances the production of mucus, which strengthens the gastrointestinal barrier against pathogens.
Step-by-step explanation:
The production of indole by Escherichia coli (E. coli) is significant in the gastrointestinal tract, as it signals host intestinal epithelial cells to tighten tight junctions and increase the production of mucus. Tightening of tight junctions is a critical process in maintaining the intestinal barrier which prevents the translocation of pathogens and toxins. The increase in mucus production by goblet cells, as part of the epithelial cell response, plays a crucial role in protecting the epithelial surface of the gastrointestinal tract against infection and physical damage by creating a barrier against pathogens.