The Fate of Bacteriophages in Recirculating Aquaculture Systems (RAS)—Towards Developing Phage Therapy for RAS

Abstract

Aquaculture production has increased tremendously during the last decades, and new techniques have been developed, e.g., recirculating aquaculture systems (RAS). In RAS, the majority of water volume is circulated via mechanical and biological filters and reused in the tanks. However, the prevention and treatment of diseases in these systems are challenging, as the pathogens spread throughout the system, and the addition of chemicals and antibiotics disrupts the microbiome of the biofilters. The increasing antibiotic resistance has made phage therapy a relevant alternative for antibiotics in food production. Indeed, as host-specific and self-replicating agent they might be optimal for targeted pathogen eradication in RAS. We tested the survival and spread of Flavobacterium columnare -infecting phage FCL-2 in recirculating aquaculture fish farm with rainbow trout (Oncorhynchus mykiss) in a fully controlled study. After a single addition, phage persisted in water samples collected from tank, fixed bed, moving bed, and aeration unit up to 14 days, and in the water of rearing tanks, rainbow trout mucus, and bioreactor carrier media from the fixed and moving bed biofilters for 21 days. Furthermore, phage adsorbed preferentially to moving bed carrier media, which contained biofilm attached and from which higher phage numbers were recovered. This study shows phages as a potent strategy for maintaining biosecurity in RAS systems.

Bacteriophages as Biocontrol Agents for Flavobacterium psychrophilum Biofilms and Rainbow Trout Infections

“… 22 These findings indicate that phages have a strong potential for use against infections caused by Flavobacterium species, particularly as phages targeting these species have shown to be able to persist in increasingly popular closed RAS. 23 …”

Phages as a Cohesive Prophylactic and Therapeutic Approach in Aquaculture Systems

“…It must be emphasized that our aforementioned experiment was performed without the involvement of fish or other aquatic organisms and, therefore, we were unable to evaluate possible therapeutic connotations in the described model [89]. Studies carried out by Almeida et al [93] have shed more light on the prophylactic value of phages tested in comparable conditions. The authors used similar phage doses (470 mL of Flavobacterium FCL-2 lysate with the titer of 2 × 10 10 pfu/mL), achieving a final phage density of 1 × 10 7 pfu/mL in each tested tank with no addition of a bacterial host.…”

An in‐vitro study on a novel six‐phage cocktail against multi‐drug resistant‐ESBL Shigella in aquatic environment

“…Water-borne bacterial pathogens can be either partially or entirely eliminated at large scale such as water storage tanks, rearing tanks, fish farms or municipal wastewater treatment storage tanks (Almeida et al 2009;Oliveira et al 2012;Silva et al 2014;Almeida et al 2019). This could be very challenging as the cell density of pathogens per volume and the physicochemical parameters on the target environments such as pH and temperature are vary case to case.…”