AggR repression by medium-chain fatty acids reduces biofilm and virulence in Enteroaggregative Escherichia coli 17-2

Enteroaggregative Escherichia coli (EAEC) is a leading cause of acute and persistent diarrhea worldwide, especially in children. A key feature of EAEC pathogenesis is the formation of a thick biofilm on the intestinal mucosa, driven by the transcriptional activator AggR, a member of the AraC/XylS family, which regulates the expression of several virulence-related genes, including aggregative adherence fimbriae (AAF). This study investigates the anti-virulence effects of fatty acids (FAs) against the prototypical EAEC strain 17-2, focusing on their potential to interfere with the regulation mediated by AggR. Growth assays demonstrated that treatment with a pool of medium- and long-chain FAs at 0.02% does not affect bacterial viability. Subsequent analysis on biofilm formation revealed that three medium-chain FAs - caprylic (C8), lauric (C12), and decenoic (C10:1) acids - significantly decrease biofilm biomass by approximately 70%. To explore the molecular mechanism, we evaluated the expression profile of aggR and aggA, showing a consistent downregulation at both transcriptional and protein levels upon treatment with each FA. Infection assays using HEp-2 cells further confirmed the phenotypic effects of FA treatment, showing reduced bacterial adherence and cytotoxicity. These findings support a model in which specific FAs reduce EAEC pathogenicity by interfering with the expression of its master regulator AggR, likely through a transcriptional mechanism. Ongoing research is investigating whether this regulation involves bacterial fatty acid sensing systems, such as FadD, or other upstream modulators of aggR. Targeting these regulatory pathways may offer novel therapeutic strategies against EAEC infections.