Abstract:
Aeromonas hydrophila infection is considered one of the most important bacterial diseases responsible for the loss of millions of dollars in the global freshwater aquaculture industry. Multidrug-resistant (MDR) A. hydrophila is becoming a global issue of concern. Non-antibiotic approaches can minimize the requirement for antimicrobials to combat infectious diseases and antimicrobial resistance. This study aims to investigate the potential application of lytic bacteriophage, ozone nanobubbles (NB-O3), a potential combination of bacteriophage and nanobubble-based technology in combatting MDR A. hydrophila in Nile tilapia. A newly Myoviridae phage pAh6.2TG was isolated, identified, and characterized in this study. The application of this phage as a prophylactic agent significantly suppressed bacterial concentration in water and improved survivability of Nile tilapia challenged with the pathogenic MDR A. hydrophila with RPS of 50 73.3%. In addition, treatments of NB-O3 in a modified recirculation system were not only safe for juvenile Nile tilapia, but also modulated fish innate immunity and significantly improved survivability of Nile tilapia challenged with MDR A. hydrophila with RPS of 64.7 - 66.7%. The surviving fish from these treatments developed specific antibody IgM against the challenged bacteria. Taken together, this study reveals that phage pAh6.2TG and NB-O3 are promising non-antibiotic approaches to control diseases caused by MDR A. hydrophila in the freshwater fish aquaculture industry. Subsequently, an investigation of the impact of nanobubble technology on bacteriophage revealed that NB-O3 killed 99.99 and 100% bacteriophage in water after 5- and 10-min treatment, respectively, while oxygen nanobubbles (NB-O2) did not. The NB-O2 treatment improved the adherence of phage pAh6.2TG on fish body surface and the uptake of phages into the fish liver. Thus, a combination of NB-O2 treatment and phage therapy is feasible to control bacterial infections in aquaculture, while NB-O3 might be a promising viral disinfection method for aquaculture water. In summary, this study demonstrates that both bacteriophage and nanobubble technology are promising strategies for combatting MDR A. hydrophila in tilapia and probably other freshwater fish species.
