Antivirulence Activity and Therapeutic Potential of Jumbo <i>Vibrio</i> Phage pVa-22 against <i>Vibrio alginolyticus</i>

<i>Vibrio alginolyticus</i> is an emerging zoonotic pathogen responsible for severe aquaculture and human infections, and its increasing antimicrobial resistance calls for alternative control strategies. Here, we report the isolation and characterization of the jumbo phage pVa-22, a phiKZ-like phage that infects <i>V. alginolyticus</i>. Morphological analysis of the phage via transmission electron microscopy revealed a large icosahedral capsid and contractile tail consistent with jumbo vibriophages. pVa-22 exhibited notable stability across broad range of temperature (4-37°C) and pH values (3-11), as well as rapid adsorption and a moderate burst-size and latent period. Host range assays revealed strong lytic activity against Vibrio species associated with foodborne illness, including <i>V. alginolyticus</i> and <i>V. parahaemolyticus</i>. Genomic analysis revealed a 233,667-bp double-stranded DNA genome encoding 242 predicted open reading frames, including multisubunit RNA polymerases and putative phage nucleus-associated proteins, which are characteristic of phiKZ-like jumbo phages. Comparative genomics demonstrated close pVa-21 relatedness but divergence in regions linked to nucleotide metabolism, tail fibers, and replication-associated genes. Functionally, pVa-22 showed weak bactericidal effects <i>in vitro</i>; however, it significantly enhanced larval survival in a <i>Galleria mellonella</i> infection model, suggesting antivirulence activity. Putative PadR-type transcriptional regulators encoded by pVa-22 may potentially influence quorum-sensing pathways, although experimental validation is required. Taken together, the findings revealed that pVa-22 is a jumbo vibriophage possessing antivirulence activity and therefore therapeutic potential, expanding the repertoire of phage-based therapeutic strategies against climate-driven <i>Vibrio</i> outbreaks.