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

## TL;DR

This study explores how a harmful bacteria, Aeromonas sp. AS1-4, affects fish and identifies beneficial intestinal bacteria that could help manage fish health in aquaculture.

## Contribution

The study identifies and characterizes potential probiotic Enterobacter strains with anti-pathogenic properties in triploid cyprinid fish.

## Key findings

- Aeromonas sp. AS1-4 infection causes oxidative damage and alters amino acid metabolism in fish.
- Three Enterobacter strains show strong probiotic traits, including biofilm inhibition and antioxidant activity.
- The identified probiotics coaggregated with pathogens and suppressed their harmful effects.

## Abstract

Our research found that Aeromonas sp. AS1-4 infection could induce severe oxidative damage in the liver and spleen of TCFs, along with a significant alteration of amino acid metabolism. Following this, we identified three probiotic isolates displaying anti-pathogenic capability and potential traits in vitro. This study provided a valuable insight into exploring the pathogenic mechanism and guiding the probiotic application in aquaculture practices.

The majority of Aeromonas 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 Aeromonas sp. AS1-4 for pathological analysis. TCFs receiving Aeromonas 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 Enterobacter strains fkY27-2, fkY84-1 and fkY84-4 were isolated from the intestine of TCFs, displaying excellent safety characteristics. In addition, intestinal Enterobacter 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 Aeromonas sp. AS1-4 and Edwardsiella tarda 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.