Efficacy of Ten Structurally Related Essential Oil Components on Anti-biofilm and Anti-quorum Sensing against Fish Spoilers Pseudomonas and Aeromonas

Biofilm formation causes persistent contamination of spoilage microorganisms, leading to serious economic losses in the aquatic processing industry. The antibacterial and anti-biofilm activity of ten carvacrol, cinnamaldehyde, and derivatives against two fish spoilers, Pseudomonas fluorescens and Aeromonas salmonicida, were evaluated by minimum inhibitory concentration (MIC), crystal violet staining, exopolysaccharide, adhesion, swimming, and swarming. Ten essential oils (EOs) tested showed different antibacterial activity, in which carvacrol and thymol exhibited the lowest MIC. Biofilms and exopolysaccharide production were repressed by all EOs at one-fourth MIC without affecting cell viability, as well as, adhesion. Swimming and swarming of two spoilage strains significantly decreased. Carvacrol and eugenol exerted the best anti-biofilm of P. fluorescens (42.2%) and A. salmonicida (62.9%), respectively. All tested EOs components showed that the decrease of acyl-homoserine lactone (AHL) quorum sensing (QS) signals of two strains were positively correlated with anti-biofilm based on violacein production. Molecular docking revealed that the most active EO, carvacrol, competed with C4-HSL to bind with receptor LuxR and AsaR by its hydroxyl group, resulting in the repression of biofilm formation. These results indicated that efficacy of antibiofilm for ten EOs was associated with the structure of compounds, and carvacrol exerted the strongest anti-biofilm activity mediated by QS against two spoilage strains.