Isolation, characterization and genomic analysis of bacteriophages for biocontrol of vibriosis caused by Vibrio alginolyticus

Vibrio alginolyticus is a significant opportunistic pathogen in marine environments, affecting both marine organisms and humans. The rise of antibiotic-resistant strains has prompted the exploration of bacteriophages as alternative biological control agents. In this study, 414 lytic bacteriophages specific to V. alginolyticus were isolated from various seafood and environmental samples. Phages P122, P125, and P160 demonstrated the broadest host range, effectively lysing 79.01 % of fish pathogenic V. alginolyticus strains and 44.69 % of environmental strains. However, no activity was observed against clinical V. alginolyticus strains or other tested species, including V. harveyi, Escherichia coli, Staphylococcus aureus, and Aeromonas hydrophila. One-step growth curve analysis revealed latent periods of 40 to 60 min and burst sizes ranging from 140 to 367 PFU/infected cells. Transmission electron microscopy (TEM) classified these phages within the class of Caudoviricetes with an icosahedral head and a long non-contractile tail. Moreover, whole-genome sequencing (WGS) identified genome sizes of approximately 76 kb, with 272-280 open reading frames (ORFs), no tRNA and pathogenic-associated genes. Comparative genomic analysis showed over 97 % similarity with other Vibrio phages. Phylogenetic analysis based on the terminase subunit also confirmed phages P122, P125, and P160 belonging to the class of Caudoviricetes. The phages were non-toxic to Galleria mellonella larvae and showed promise in reducing mortality rates when used as a cocktail treatment. The study highlights the potential of these phages as effective biocontrol agents in aquaculture, offering a promising alternative to antibiotics for managing Vibrio infections.