Bacteriophage PVN06 protected catfish Pangasianodon hypophthalmus from Edwardsiella ictaluri infection.

Bacillary necrosis of pangasius (BNP) is a disease caused by Edwardsiella ictaluri bacteria in striped catfish Pangasianodon hypophthalmus that results in high mortality rates. To control this disease, bacteriophages have been considered as alternatives to antibiotics. In this study, we applied the lytic bacteriophage PVN06 in striped catfish fingerlings to prevent E. ictaluri infection. In an experimental trial, the phage was administered to fish by feeding phage-coated feed with doses of 7.17±0.09, 8.17±0.09 and 9.17±0.09 log PFU/g feed per day before bacterial infection. Fish were infected by bacteria once with concentrations ranging from 3.01 to 7.01 log CFU/ml tank water. A day after infection, phage treatment resumed at a rate of once per day until the end of the trial. The results of the trial show that bacterial infection caused typical symptoms of BNP in fish with the cumulative fish death rate of 36.7±2.9 to 75.0±5.0%, depending on the bacterial concentration used for infection. Phage treatment with 9.17±0.09 log PFU/g significantly reduced the mortality rate, while treatments with 8.17±0.09 and 7.17±0.09 log PFU/g did not. This phage dose resulted in a 61.7-fold reduction in the toxicity of the bacterial pathogen and the survival rate of 15-23.3% in fish. Our study has demonstrated that the bacteriophage PVN06 protected striped catfish from BNP.

Selection of Phages to Control Aeromonas hydrophila - An Infectious Agent in Striped Catfish.

Striped catfish (Pangasianodon hypophthalmus) farming in the Mekong Delta Vietnam (MKDVN) importantly contributes to national aquaculture export. Currently, however, diseases occur more frequently across the entire MKDVN region. One of the most common types is hemorrhagic septicemia caused by Aeromonas hydrophila. In this study, isolation and selection of the phages for control in vitro Aeromonas hydrophila were conducted. 24 phages were isolated from 100 striped catfish pond water samples. Next, lytic activity of these phages was clarified. Four phages with short latent period (about 25 to 40 min) and/or high burst size (about 67 to 94 PFU/ cell) were selected to evaluate their infection activity to different phage-resistant A. hydrophila strains. Two phages termed as TG25P and CT45P were subjected to the phage cocktail to inactivate A. hydrophila. Re-growth of the host bacteria appeared about eight hours after treatment. Usage of the phage cocktail that attach different host bacterial receptors is not always much effective than usage of single phage. This is the first report about phage therapy to control A. hydrophila isolated from striped catfish. Some challenges in the phage cocktail were shown to achieve strategies in prospective studies in the context of high antibiotic resistance of A. hydrophila.