Influence of environmental variables in the efficiency of phage therapy in aquaculture

Abstract

Aquaculture facilities worldwide continue to experi-ence significant economic losses because of disease caused by pathogenic bacteria, including multidrug-resistant strains. This scenario drives the search for alternative methods to inactivate pathogenic bacteria. Phage therapy is currently considered as a viable alternative to antibiotics for inactivation of bacterial pathogens in aquaculture systems. While phage therapy appears to represent a useful and flexible tool for microbiological decontamination of aquaculture effluents, the effect of physical and chemical proper-ties of culture waters on the efficiency of this tech-nology has never been reported. The present study aimed to evaluate the effect of physical and chemical properties of aquaculture waters (e.g. pH, tempera-ture, salinity and organic matter content) on the efficiency of phage therapy under controlled experi-mental conditions in order to provide a basis for the selection of the most suitable protocol for subse-quent experiments. A bioluminescent genetically transformed Escherichia coli was selected as a model microorganism to monitor real-time phage therapy kinetics through the measurement of bioluminescence, thus avoiding the laborious and time-consuming conventional method of counting colony-forming units (CFU). For all experiments, a bacterial concentration of ≈ 10 5 CFU ml −1 and a phage concentration of ≈ 10 6–8 plaque forming unit ml −1 were used. Phage survival was not significantly affected by the natural variability of pH (6.5–7.4), temperature (10–25°C), salinity (0–30 g NaCl l −1) and organic matter concentration of aquaculture waters in a tem-perate climate. Nonetheless, the efficiency of phage therapy was mostly affected by the variation of salin-ity and organic matter content. As the effectiveness of phage therapy increases with water salt content, this approach appears to be a suitable choice for marine aquaculture systems. The success of phage therapy may also be enhanced in non-marine systems through the addition of salt, whenever this option is feasible and does not affect the survival of aquatic species being cultured.