Study of cocktail phage infecting Aeromonas dhakensis isolated from striped catfish (Pangasianodon hypophthalmus) in Vietnam
Aeromonas dhakensis has emerged as a major pathogen causing motile Aeromonas septicemia (MAS) in striped catfish (Pangasianodon hypophthalmus), yet it is frequently misidentified as A. hydrophila, leading to underestimation of its prevalence in aquaculture. This study accurately identified A. dhakensis isolates from diseased catfish in the Mekong Delta, Vietnam, confirming its dominance in local outbreaks. To develop an alternative control strategy to antibiotics, 30 lytic bacteriophages were isolated from aquaculture ponds and screened against 16 A. dhakensis strains. Two highly virulent phages, DT94P2 and AG31P3, exhibited broad host ranges and high virulence indices. Phage cocktails combining DT94P2 with AG31P3 demonstrated synergistic lytic activity and effectively lysed previously resistant bacterial strains. These findings represent the first genomic characterisation of A. dhakensis-specific lytic phages in Vietnamese striped catfish aquaculture and highlight their potential use as safe, targeted agents for phage therapy to reduce antibiotic dependence in tropical aquaculture systems.