Avian Pathogenic Escherichia coli (APEC) poses a significant threat to the global poultry industry and has also zoonotic potential, meaning it could infect humans. One critical factor in APEC infection is its ability to adhere to host tissues, a process mediated by a protein called FdeC among others. This protein is present in pathogenic E. coli strains but is often nonfunctional in nonpathogenic ones. Our study focused on understanding the role of FdeC in APEC's ability to bind to chicken intestinal cells. Through an extensive screen of 2000 transposon mutants from the APEC IMT5155 strain, we discovered that a specific mutation in the fdeC gene led to enhanced adhesion. However, a direct deletion of the fdeC gene did not produce the same effect under standard conditions, which led us to investigate the environmental factors that might regulate FdeC expression. We found that FdeC's expression is highly dependent on the environmental conditions such as temperature and pH. Using optimized conditions for FdeC expression, we observed significantly higher adhesion and motility levels in the fdeC-deleted IMT5155 strain compared to the wild type. To understand the mechanisms behind this, we employed mass spectrometry and discovered that the absence of FdeC led to changes in ion transport and downregulated a protein called YbjN, which usually inhibits bacterial movement. Collectively, our findings suggest that FdeC has host-dependent expression and contributes to enhancement of bacterial fitness by modulating motility during colonization.