Antibacterial mechanism of lactobionic acid against Aeromonas salmonicida by transcriptomic analysis and its application in refrigerated grass carp

Aeromonas salmonicida is ubiquitously distributed in aquatic environments and is one of the major pathogens of freshwater aquaculture fish. Recent studies have demonstrated that A. salmonicida plays a crucial role in fish spoilage. In this study, a novel antibacterial agent, lactobionic acid (LBA), was investigated for its antibacterial effect against A. salmonicida. The results showed that the minimum inhibitory concentration (MIC) of LBA was 16 mg/mL. Bacterial cells dropped below the detection limit within 2 h after exposure to 2 MIC of LBA. The cells treated with LBA became rough and sunken, and LBA caused cellular protein leakage and an increase in conductivity. Transcriptomic analysis exhibited that the expression of 1273 genes in A. salmonicida was altered by LBA, including 700 down-regulated and 573 up-regulated genes. The most representative down-regulated genes were enriched in bacterial chemotaxis, two-component system and ATP-binding cassette transporter pathways. LBA showed an effective inhibitory effect on A. salmonicida in refrigerated grass carp and could prolong the storage time of grass carp. Overall, the intervention of LBA resulted in the decrease of cell chemotaxis and disturbance of cellular metabolic processes, which inhibited A. salmonicida. These results revealed the antibacterial mechanism of LBA against A. salmonicida, which provided a strategy for the control of fish spoilage.