Abstract
Aquaculture facilities worldwide continue to experience 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 properties of culture waters on the efficiency of this technology has never been reported. The present study aimed to evaluate the effect of physical and chemical properties of aquaculture waters (e.g. pH, temperature, salinity and organic matter content) on the efficiency of phage therapy under controlled experimental conditions in order to provide a basis for the selection of the most suitable protocol for subsequent 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 ≈ 105 CFU ml−1 and a phage concentration of ≈ 106–8 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 temperate climate. Nonetheless, the efficiency of phage therapy was mostly affected by the variation of salinity 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.
Highlights
One-third of the world seafood supply comes from aquaculture, the fastest growing food animal-producing sector worldwide (FAO, 2012)
Often suffers from heavy financial losses because of mass mortality caused by bacterial infection, including those promoted by multidrug-resistant bacteria that are transmitted through the water and able to infect a great variety of aquaculture species (Almeida et al, 2009)
The results of this study suggest that bacteria that restarted to grow after phage therapy were not resistant to the phage
Summary
One-third of the world seafood supply comes from aquaculture, the fastest growing food animal-producing sector worldwide (FAO, 2012). In order to prevent possible diseases in aquaculture, producers often use antibiotics This practice is currently discouraged and kept to a minimum in order to avoid the development of drug-resistant bacteria. To overcome the risks of development and spreading of antibiotic-resistant bacteria, it is urgent to develop more environmentally friendly methods to control disease in aquaculture. In line with this idea, the use of phage therapy seems to be a very promising technique, as bacterial diseases are a major problem in the expanding aquaculture industry (Wahli et al, 2002; Berthe, 2005; Almeida et al, 2009)
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