Molecular insights into gallic acid as a quorum sensing inhibitor targeting the LuxS/AI-2 system in Escherichia coli O157: H7 and its antibiofilm applications

The quorum sensing (QS) system is a critical drug target that regulates the toxins production and biofilms formation in pathogens. This study elucidates the mechanism by which the plant polyphenol gallic acid (GA) acts as a QS inhibitor targeting the LuxS/AI-2 system in Escherichia coli O157: H7, and evaluates its potential for antibiofilm applications. Results show that GA broadly interferes with the transcription of genes in the AI-2 synthesis pathway and inhibits AI-2 production. Molecular docking combined with in vitro enzymatic inhibition assays identified LuxS as a key target of GA. Thermodynamically favored, GA binds to LuxS via hydrogen bonds and van der Waals interactions, forming a stable ground-state complex that alters the enzyme's secondary structure and inhibits its activity. Further mechanistic analysis indicates that GA induces conformational changes in the protein, reduces active site volume, and restricts key catalytic residues, thereby blocking substrate access. Under simulated meat broth conditions, GA significantly enhances the biofilm-inhibitory effect of conventional disinfectants even at subinhibitory concentrations on food-contact surfaces. These findings provide theoretical support for the potential utilization of GA as a QS-targeted antibiofilm adjuvant in the food industry.