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

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  • Funding Information This work was supported by funding FEDER through COMPETE – Programa Operacional Factores de Competitividade, and by National funding through FCT-Fundação para a Ciência e Tecnologia (Foundation for Science and Technology), within the research project FCOMP-01–0124-FEDER-013934 and project PROMAR 31-03-05-FEP-0028. We also thank Centre for Environmental and Marine Studies, University of Aveiro (CESAM, project Pest-C/MAR/LA0017/2011) and Department of Biology of University of Aveiro where this work was done. Financial support to Silva Y.J. (SFRH/BD/65147/2009) and Pereira C. (SFRH/BD/76414/2011) was provided by the FCT in the form of PhD grants. Financial support to Costa L. was provided in the form of PI grant within the research project FCOMP-01–0124-FEDER-013934.

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.

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