Gut Microbiota Divergence Drives Aeromonas Hydrophila Resistance in Common Carp (Cyprinus carpio): Probiotic Role of...

Bacterial diseases pose significant constraints on the sustainability of aquaculture, with Aeromonas hydrophila (A. hydrophila) emerging as a critical threat to freshwater fish populations. The gut microbiota significantly influences host health and disease resistance, however, the specific mechanisms by which the gut microbiota enhances pathogen defense remain unclear. In this study, we utilized the common carp (Cyprinus carpio) as a model organism to investigate the contribution of the intestinal microbiota to host resistance to A. hydrophila infection. Fish were categorized into resistant (S group) and susceptible (T group) groups on the basis of postinfection survival outcomes. Specifically, group S presented significantly greater activity of acid phosphatase (ACP), alkaline phosphatase (AKP), and lysozyme (LZM) and greater expression of immune-related genes (il-1β, tnfα, il-8, il-10, and tgfβ) and intestinal barrier markers (zo-1, occludin, and claudin1) than did group T. Further analysis revealed substantial differences in the gut microbial composition between the two groups, with Cetobacterium identified as a key differentiating genus. Anaerobic culture techniques enabled the isolation of Cetobacterium somerae LJ-1 from the common carp intestine. Subsequent feeding trials demonstrated that dietary supplementation with Cetobacterium significantly enhanced the expression of immune-related genes in the intestine and kidney, increased the activities of ACP, AKP, and LZM in the intestine, and promoted the expression of intestinal barrier-related genes. Moreover, infection challenge experiments confirmed that Cetobacterium supplementation reduced A. hydrophila loads in internal tissues and significantly improved survival rates. Overall, this study provides theoretical and technical support for utilizing native intestinal microbiota to prevent bacterial infections and promote sustainable aquaculture development.