Isolation of a Virulent subsp. Bacteriophage and Its Application in Phage Therapy in Turbot ().

Aeromonas salmonicida is an aquatic pathogen that can infect a variety of fish. Phage therapy has been applied to treat bacterial infections. In this study, we obtained three subsp. phage isolates from sewage, and one phage (vB_AsM_ZHF) exhibited the best antibacterial effect, based on kinetics experiments. Sequencing indicated that the vB_AsM_ZHF genome is 161,887 bp (41.24% C+G content) with 237 predicted open reading frames. No antibiotic resistance or virulence genes were detected in the complete genome, which is a requirement for phage therapy safety. Intraperitoneal injection of phage vB_AsM_ZHF into turbot at 8 × 10 PFU/fish rescued turbot from subsp. injection and reduced the bacterial burden by 1 order of magnitude. Injection of vB_AsM_ZHF also decreased levels of inflammatory cell infiltration in muscle tissue, cytokines interleukin-1β (IL-1β), tumor necrosis factor alpha (TNF-α), and gamma interferon (IFN-γ) in serum and the expression of the inflammatory factors IL-1β, IL-6, IFN-γ, transforming growth factor β, TNF-α, and hepcidin in the liver, spleen, and head kidney of turbot. Phage vB_AsM_ZHF demonstrated antibacterial ability and and significantly reduced mortality in turbot challenged by subsp. . This study revealed that phage vB_AsM_ZHF can effectively treat the infection caused by subsp. in turbot. is an aquatic pathogen that can infect different fish and causes economic loss to the global aquaculture industry. Clinical strains of have developed multidrug resistance, and phage therapy is being evaluated for controlling bacterial infections. Phages are biological antibacterial agents and have the potential to be therapeutic agents against multidrug-resistant bacteria. In this study, three subsp. phages were isolated from sewage, and their biological behaviors were characterized. The newly isolated phage vB_AsM_ZHF could inhibit subsp. infection and , suggesting that it may be an alternative strategy to antibiotics for protecting fish against multidrug-resistant subsp. in the aquaculture industry.