Phage cocktail against Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease (AHPND) in Penaeus vannamei: Genomic, biological, and pathological characterization.

Phages vB_Pd_PDCC-1, vB_Vc_SrVc9, and vB_Vp_PvVp11 were found to be lytic against Vibrio parahaemolyticus acute hepatopancreatic necrosis disease (AHPND) and other pathogenic vibrios. The complete genomic and biological characterization of phage vB_Vp_PvVp1 was conducted, and a cocktail of these three phages was applied to juvenile Penaeus vannamei infected with V. parahaemolyticus AHPND. Water samples collected during the challenges were analyzed using metagenomics. At the end of the experimental infection, the phage cocktail did not improve shrimp survival compared to the positive control group (infected only with bacteria). This suggests the emergence of phage-resistant V. parahaemolyticus strains. However, a significantly lower mortality rate was observed 12 h post-infection, along with a shortening of the disease course in the phage therapy treatment. A phage-resistant strain of V. parahaemolyticus AHPND was in vitro isolated. For the first time, we report the identification of nucleotide variants in the glycosyltransferase gene of this mutant strain through genome sequencing. Although the phage cocktail was ineffective in controlling AHPND, some protective benefits of phage therapy were noted in P. vannamei during the acute phase-the most critical stage-compared to the positive control. Phage therapy decreased alpha diversity and altered the microbiota composition during the challenge, increasing V. parahaemolyticus. The Vibrio AHPND pathogen produces a potent PirAB toxin, making this disease difficult to manage. Further studies are needed to explore synergistic approaches as effective therapeutic tools.