Effect of phage therapy on survival, histopathology, and water microbiota of Penaeus vannamei challenged with Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease (AHPND)

Abstract

Shrimp farming production is affected severely by the presence of toxigenic strains of Vibrio parahaemolyticus, the leading etiological agent of acute hepatopancreatic necrosis disease that causes as much as 100% mortality. To date, conventional methods have not effectively controlled AHPND, and only a few studies have reported bioassays testing phage therapy against this shrimp disease, none with a metagenomic approach. Here, Penaeus vannamei juveniles infected with AHPND-causing Vibrio parahaemolyticus were treated with phage to assess shrimp survival, tissue damage, as well as water microbiota dynamics. Phage therapy reduced by 4% shrimp mortality compared to the positive control. Histopathological analysis showed a 3 h delay in mortality of shrimp in the acute stage treated with phage therapy concerning the positive control, as well as a shortening of the terminal phase. Further, surviving shrimp in the terminal stage were only found in the positive control treatment. No significant differences were observed in the diversity of water microbiota between these treatments. Interestingly, V. parahaemolyticus caused up to 65% mortality, although its density decreased rapidly, and its relative abundance in the water microbiota ranged from 0.1% to 0.4%, while the marine bacteria that predominated in the microbiota was Donghicola eburneus (25.2%–54.6%). In addition, two copies of the pVA1 plasmid per V. parahaemolyticus genome were detected during the first 12 hpi in the positive control and phage therapy treatments. Phage therapy using a single phage could not effectively control AHPND in this investigation. Therefore, methods combining different approaches to prevent or treat the AHPND, such as a phage cocktail and a toxin binder, should be considered to increase the success rate in mitigating the disease.