Antibacterial Activity of Berberine Against Aeromonas hydrophila and Associated Transcriptional Reprogramming

Berberine (BBR), a plant-derived isoquinoline alkaloid, exhibits broad-spectrum antibacterial activity, but its molecular mechanisms against Aeromonas hydrophila remain unclear. This study investigated the antibacterial action and underlying mechanisms of BBR against A. hydrophila through integrated phenotypic assays and transcriptomic analysis. BBR showed notable antibacterial activity with a minimum inhibitory concentration (MIC) of 2.5 g/L. Treatment at a sub-inhibitory concentration (1/2 MIC) severely compromised cell membrane integrity, evidenced by increased leakage of alkaline phosphatase (AKP) and β-galactosidase (β-GAL). Transmission electron microscopy (TEM) revealed ultrastructural damage including plasmolysis and membrane rupture. RNA-seq analysis identified 740 differentially expressed genes (DEGs). Crucially, BBR extensively downregulated core energy metabolism and catabolic pathways, including the TCA cycle, fatty acid β-oxidation, and amino acid degradation. Concurrently, genes associated with flagellar assembly and DNA repair were upregulated. These findings reveal that BBR exerts its antibacterial effect via a multi-target mechanism involving direct physical damage to the cell envelope and the suppression of central metabolism. This study elucidates the antibacterial effects of BBR against A. hydrophila and provides a foundation for its potential use as an eco-friendly agent in aquaculture.