Phage pAEv1: A potential biocontrol agent against <i>Aeromonas veronii</i> infections

<i>Aeromonas veronii</i>, a significant aquaculture pathogen, induces substantial mortality in farmed aquatic species. Given the therapeutic promise of phage-mediated bacterial lysis, we isolated <i>A. veronii</i> from contaminated aquaculture systems and characterized its biological properties. Concurrently, the phage pAEv1 was recovered from the same aquatic environment using the pathogen as a host. Biological characterization revealed an optimal multiplicity of infection (MOI) of 0.01, a 10-min latent period, and a titer of 1.3 × 10⁸ PFU/mL. pAEv1 exhibited notable stability, maintaining infectivity at temperatures ranging from -80°C to 55°C and pH levels of 5-9. Genomic analysis identified a circular double-stranded DNA genome, closely related to the <i>Aeromonas</i> phage pAEv1812 (ID: OL964754.1), with UniProtKB-based functional annotation categorizing encoded proteins into DNA modification and structural classes. COG and KEGG analyses further demonstrated gene enrichment in nucleic acid metabolism and purine biosynthesis, consistent with phage replication machinery. Crucially, virulence factor screening confirmed the absence of resistance or virulence genes, ensuring genetic-level biosafety. <i>In vitro</i> antimicrobial tests showed that phage pAEv1 effectively inhibited <i>A. veronii</i>. Additionally, <i>in vivo</i> experiments demonstrated that grass carp treated with pAEv1 had an 80% survival rate after 7 days of exposure to a double minimum lethal dose (MLD) of the bacterium.