Punicalagin Inhibits Salmonella Virulence Factors and Has Anti-Quorum-Sensing Potential
ABSTRACTPunicalagin, an essential component of pomegranate rind, has been demonstrated to possess antimicrobial activity against several food-borne pathogens, but its activity on the virulence of pathogens and its anti-quorum-sensing (anti-QS) potential have been rarely reported. This study investigated the efficacy of subinhibitory concentrations of punicalagin onSalmonellavirulence factors and QS systems. A broth microdilution method was used to determine the MICs of punicalagin for 10Salmonellastrains. Motility assay and quantitative reverse transcription (RT)-PCR were performed to evaluate the effects of punicalagin on the virulence attributes and QS-related genes ofSalmonella. The MICs of punicalagin for severalSalmonellastrains ranged from 250 to 1,000 μg/ml. Motility assays showed that punicalagin, at 1/16× MIC and 1/32× MIC, significantly decreased bacterial swimming and swarming motility, which corresponded to downregulation of the motility-related genes (fliA,fliY,fljB,flhC, andfimD) in RT-PCR assays. RT-PCR also revealed that punicalagin downregulated the expression of most of the selected genes involved inSalmonellavirulence. Moreover, a QS inhibition assay indicated that punicalagin dose dependently inhibited the production of violacein byChromobacterium violaceumand repressed the expression of QS-related genes (sdiAandsrgE) inSalmonella. In addition, punicalagin significantly reducedSalmonellainvasion of colonic cells (P< 0.01) with no impact on adhesion. These findings suggest that punicalagin has the potential to be developed as an alternative or supplemental agent for prevention ofSalmonellainfection.