Abstract
Flavobacterium columnare, the causative agent of columnaris disease in fish, causes millions of dollars of losses in the US channel catfish industry alone, not to mention aquaculture industry worldwide. Novel methods are needed for the control and treatment of bacterial diseases in aquaculture to replace traditionally used chemotherapies. A potential solution could be the use of phages, i.e., bacterial viruses, host-specific and self-enriching particles that can be can easily distributed via water flow. We examined the efficacy of phages to combat columnaris disease. A previously isolated phage, FCL-2, infecting F. columnare, was characterized by sequencing. The 47 142 bp genome of the phage had G + C content of 30.2%, and the closest similarities regarding the structural proteins were found in Cellulophaga phage phiSM. Under controlled experimental conditions, two host fish species, rainbow trout (Oncorhynchus mykiss) and zebrafish (Danio rerio), were used to study the success of phage therapy to prevent F. columnare infections. The survival of both fish species was significantly higher in the presence of the phage. Hundred percent of the zebrafish and 50% of the rainbow trout survived in the phage treatment (survival without phage 0 and 8.3%, respectively). Most importantly, the rainbow trout population was rescued from infection by a single addition of the phage into the water in a flow-through fish tank system. Thus, F. columnare could be used as a model system to test the benefits and risks of phage therapy on a larger scale.
Highlights
In 2014, the WHO (2014) reported high rates of antimicrobial resistance in common diseasecausing bacteria in all regions of the world
Concerns of antibiotic resistance have brought attention to the large amounts of antibiotics used in animal production, in aquaculture (Buschmann et al, 2012; Hollis and Ahmed, 2013)
Using FCL-2, it was shown that phages have great potential in controlling columnaris disease in smallscale experimental systems, and in rainbow trout populations in flow-through tanks
Summary
In 2014, the WHO (2014) reported high rates of antimicrobial resistance in common diseasecausing bacteria in all regions of the world. Concerns of antibiotic resistance have brought attention to the large amounts of antibiotics used in animal production, in aquaculture (Buschmann et al, 2012; Hollis and Ahmed, 2013). Antibiotics used in aquaculture may dissolve from the fish feed to the surrounding water (Cabello et al, 2013), enabling the development of antibiotic resistance in environmental microbes (Buschmann et al, 2012; Di Cesare et al, 2013). The risk of development of phage resistance in the target bacteria needs to be considered, by e.g., using multiphage cocktails, phage therapy has great potential in the treatment of aquatic organisms. Phages are host-specific and self-enriching particles that can be can distributed via water flow within rearing units
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