Analysis of the antibacterial mechanism and antivirulence efficacies of citral against Shewanella putrefaciens and Pseudomonas fluorescens in mono- and co-culture

Citral exerted its antibacterial activities in a dose-dependent manner in the three groups. • Citral increased intracellular oxidative stress levels of S. putrefaciens and P. fluorescens in mono- and co-culture. • Citral reduced motility and weakened biofilm formation of S. putrefaciens and P. fluorescens in mono- and co-culture. • Citral treatment can prolong the shelf life of large yellow croaker. Shewanella putrefaciens and Pseudomonas fluorescens , as significant specific spoilage organisms in aquatic products, can regulate cell density and a variety of physiological processes through quorum sensing (QS). This research examined the antibacterial mechanism and antivirulence efficacies of citral (CT), as a quorum sensing inhibitor (QSI), against S. putrefaciens and P. fluorescens in mono- and co-culture. Furthermore, the application of CT to large yellow croaker preservation was investigated. Results revealed that CT exerted its antibacterial activities in a dose-dependent manner. CT increased intracellular oxidative stress levels and malondialdehyde (MDA) content, decreased ATP content and peroxidase activity, and promoted the damage of cell membrane, especially in S. putrefaciens group. These two bacteria had a synergistic effect in causing spoilage through biofilm formation and motility. The antivirulence efficacies of CT against the co-culture group were weaker than those of in the mono-culture groups. CT was also found to suppress the expression of key virulence regulators in S. putrefaciens and P. fluorescens virulence, including Autoinducers-2 (AI-2) production in the QS system. Furthermore, CT had the potential capability in the preservation of large yellow croaker. Consequently, these results proved CT could combat bacteria and had antivirulence efficacies against S. putrefaciens and P. fluorescens in mono- and co-culture. Download: Download high-res image (183KB) Download: Download full-size image