Quorum-sensing inhibition by hexanal in biofilms formed by Erwinia carotovora and Pseudomonas fluorescens

To prevent the spoilage of vegetables in food processing, hexanal, a quorum-sensing (QS) inhibitor, was first used to inhibit the formation of Erwinia carotovora and Pseudomonas fluorescens biofilms. Their growth curves were not markedly inhibited by hexanal below the minimum inhibitory concentration (MIC), but the biofilm formation could be inhibited. Motility, exopolysaccharide production, and biofilm formation of E. carotovora and P. fluorescens were significantly inhibited by hexanal at sub-MICs (P < 0.05). There was a positive dose-dependent relationship (r = 0.8167–0.9998) between the inhibition ratio and concentrations of hexanal during the critical biofilm-formation stage (1–3 d), as well as a negative relationship (r = −0.8168 to −0.9998) between the inhibition ratio and culture time. The biomass, as well as average and maximum of biofilm thicknesses, decreased significantly (P < 0.05) relative to those of the control group. Luminescence, which represents the AI-2 molecule, decreased significantly with the increase in hexanal concentration (P < 0.05), indicating that inhibition of motility, exopolysaccharide production, and biofilm formation of E. carotovora and P. fluorescens was related to the decrease in the autoinducer AI-2. Therefore, hexanal could be developed as a new QS inhibitor for preventing decay of vegetables in the food industry.