Triploid Cyprinid Fish (TCF) Under Aeromonas sp. AS1-4 Infection: Metabolite Characteristics and In Vitro Assessment of Probiotic Potentials of Intestinal Enterobacter Strains

The majority of <i>Aeromonas</i> strains are opportunistic pathogens for both humans and animals, causing a variety of diseases and posing a considerable risk to their health. In the current study, triploid cyprinid fish (TCF) were infected with a novel pathogenic <i>Aeromonas</i> sp. AS1-4 for pathological analysis. TCFs receiving <i>Aeromonas</i> sp. AS1-4 challenge exhibited oxidative damage in the liver and spleen, along with significant changes in immune-related gene expressions. Metabolomics assay indicated that strain AS1-4 challenge may exhibit a significant impact on metabolic processes of amino acids, with methylsuccinic acid (MSA) identified as vital biomarker. Following that, three potential probiotics designated <i>Enterobacter</i> strains fkY27-2, fkY84-1 and fkY84-4 were isolated from the intestine of TCFs, displaying excellent safety characteristics. In addition, intestinal <i>Enterobacter</i> strains exhibited multiple probiotic traits, including high degrees of hydrophobic activity, aggregation performance, biofilm-forming activity (BFA) and nutrient decomposing ability. Moreover, these probiotic isolates markedly coaggregated with <i>Aeromonas</i> sp. AS1-4 and <i>Edwardsiella tarda</i> 1l-4 and then suppressed their pathogenic biofilm-forming abilities, along with possessing robust antioxidant potential against various free radicals. These findings may provide valuable insights into metabolic response in fish post infection and health management in aquaculture.