Characterization and genome analysis of lytic Vibrio phage VPK8 with potential in lysing Vibrio parahaemolyticus isolates from clinical and seafood sources.

Background: Vibrio parahaemolyticus is a marine bacterium causing seafood-associated gastrointestinal illness in humans and acute hepatopancreatic necrosis disease (AHPND) in shrimp. Bacteriophages have emerged as promising biocontrol agents against V. parahaemolyticus. This study characterizes Vibrio phage VPK8, focusing on host specificity, efficiency of plating (EOP) variability across V. parahaemolyticus isolates from diverse sources and other Vibrio species, morphology, genomic features, and bacteriolytic potential.

Methods: Vibrio phage VPK8 was isolated from blood cockles in Thailand using a mixed-host approach and purified via the double-layer agar method. Host specificity was evaluated using spot assays and EOP measurements against 120 Vibrio strains, including AHPND-associated, clinical, and seafood isolates. Phage morphology was characterized by transmission electron microscopy (TEM), while genomic features were analyzed using next-generation sequencing. Lytic characteristics, including latent period and burst size, were determined through one-step growth curves, and bacterial growth reduction was evaluated over a 24-h.

Results: Vibrio phage VPK8 is a lytic phage with a 42,866 bp linear double-stranded genome, G + C content of 49.4%, and 48 coding sequences. Phylogenetic analysis grouped it within the Autographiviridae family, showing 95.96% similarity to Vibrio phage vB_VpaP_MGD1. Viral proteomic analysis placed VPK8 within the Pseudomonadota host group. Spot assays indicated broad lytic activity, but EOP analysis revealed high infectivity in clinical and seafood V. parahaemolyticus isolates, as well as some V. cholerae and V. mimicus strains. TEM revealed an icosahedral head (~ 60 nm) and a short tail. At a multiplicity of infection of 0.01, VPK8 exhibited a latent period of 25 min, a burst size of 115, and effectively inhibited the reference host V. parahaemolyticus PSU5124 within 6 h, maintaining its lytic activity and stability for over 24 h.

Conclusions: This study provides a detailed characterization of Vibrio phage VPK8 which exhibits targeted infectivity with high EOP in clinical and seafood V. parahaemolyticus isolates, as well as selected Vibrio species. Its stable lytic performance, rapid replication, and genomic safety suggest its potential for phage-based applications. Further studies should explore its in vivo efficacy and the genetic features contributing to phage resistance mechanisms, enhancing its potential applicability in managing Vibrio-related diseases.