Genomic overview of the N4-like TEMp-D1 phage and the efficacy of antibiotic-phage synergy for the biocontrol of Photobacterium damselae subsp. damselae

Photobacterium damselae subsp. damselae (PDD) is a pathogenic bacterium that affects both marine animals and humans. It poses a significant problem for aquaculture and a threat to public health. Phages are considered potential therapeutics due to their high specificity against pathogens and environmental friendliness. The Phage-Antibiotic Synergy (PAS) approach has recently shown strong potential as an alternative strategy to overcome the resistance of bacteria to both phages and antibiotics. In this study, we investigated the genomic characteristics of the TEMp-D1 phage, which specifically infects PDD, and the effects of different environmental conditions on phage stability. The genome of TEMp-D1 is 72,582 bp in length with a GC content of 55.1%. Sequence analysis revealed 97 potential coding sequences (CDS) with an N4-like genomic organization. Phylogenetic analysis using the whole genome proteomic tree and the amino acid sequence of the large terminase subunit showed a close relationship between TEMp-D1 and phages infecting Vibrio and Pseudomonas species. Furthermore, the effects of PAS were examined using sublethal doses (1/4 MIC) of four antibiotics (oxytetracycline, florfenicol, sulfadiazine-trimethoprim, and enrofloxacin) and the TEMp-D1 phage on in vitro PDD biofilm formation and cell growth. Inhibition rates were significantly higher in the PAS-treated groups compared to those treated with phage or antibiotics alone. These results demonstrate the potential of TEMp-D1 and antibiotic combinations for use against PDD in aquaculture and other in vivo applications.