Effects of Oral Application of Bacteriophage Cocktails to Treat Aeromoniasis Caused by Aeromonas hydrophila

Aeromonas hydrophila is a prominent pathogen of freshwater fish. Antimicrobials can be used to treat Motile Aeromonas septicemia (MAS) caused by A. hydrophila. However, bacteria may become resistant to these drugs, and antimicrobials could pollute water. Innovative eco-friendly approaches must be developed to avoid and address MAS. The present study used bacteriophage cocktails to treat rainbow trout infected with MAS. Fish were administered an oral cocktail of Aquaneticvirus APT65, AP-Y28, AP-T5, and AP-ATCC phages to evaluate the therapeutic efficacy of phage therapy against A. hydrophila-induced fish mortality. The survival of Aquaneticvirus APT65 phage in fish organs was also evaluated over an 8-day study period. Aquaneticvirus APT65 phage was found in fish internal organs, demonstrating that the phage may cross the intestinal barrier. In challenge trials with the LD70 dosa of A. hydrophila, phage cocktail doses of lx108 PFU/g feed reduced mortality in rainbow trout by 32-44.8%. Phage treatment prior to infection significantly increased fish survival compared to treatment after one day of infection. Relative percent survival results showed that oral phage cocktails protected fish against A. hydrophila mortality in a time-dependent way. This study is valuable for fanner-level application because it includes simple, practical procedures for phage cocktail formulation, medicated feed preparation, and oral administration, as well as data on phage survival and protection data.