A novel bacteriophage pAEh1 for controlling Aeromonas hydrophila infection in aquaculture.

Aeromonas hydrophila is a significant pathogen in aquaculture, causing elevated mortality in cultured species. Bacteriophages, known for their specificity, have emerged as promising antimicrobial agents. In this study, the biological characteristics of A. hydrophila were examined, revealing hemolytic activity and multi-drug resistance. A bacteriophage, pAEh1, was isolated from aquaculture water using A. hydrophila as the host. Biological characterization identified it as a member of the Siphoviridae family. Functional annotation of its proteins classified them into categories including transcription, DNA assembly and modification, host lysis, structural proteins, host recognition, and resistance to host defenses. No resistance or virulence-related genes were detected, supporting the biosafety of phage pAEh1 at the genetic level. In vitro antibacterial assays confirmed its effective inhibitory activity against A. hydrophila. In vivo therapeutic trials showed that grass carp treated with pAEh1 achieved a 70 % survival rate seven days after challenge with double the minimum lethal dose, highlighting its potential for controlling A. hydrophila infections. Infection with A. hydrophila caused severe histopathological damage in the liver, spleen, and kidneys of grass carp, which was significantly alleviated by phage pAEh1 therapy. Serum biochemical analysis indicated that pAEh1 treatment helped restore key metabolic parameters to near-normal levels. 16S rDNA sequencing revealed that A. hydrophila infection induced intestinal microbiota dysbiosis, characterized by an enrichment of pathogenic genera. The pAEh1 treatment effectively mitigated this dysbiosis, reduced pathogenic bacteria, and promoted the recovery of beneficial bacteria, thereby restoring the microbial community structure and function to a state resembling that of healthy fish. These findings demonstrate that pAEh1 therapy protects against infection-induced tissue damage and restores intestinal homeostasis. Collectively, these results provide a strong theoretical basis for the application of phage pAEh1 in preventing A. hydrophila outbreaks in aquaculture.