Comparison of Delivery Methods in Phage Therapy against Flavobacterium columnare Infections in Rainbow Trout

Abstract

Viruses of bacteria, bacteriophages, specifically infect their bacterial hosts with minimal effects on the surrounding microbiota. They have the potential to be used in the prevention and treatment of bacterial infections, including in the field of food production. In aquaculture settings, disease-causing bacteria are often transmitted through the water body, providing several applications for phage-based targeting of pathogens, in the rearing environment, and in the fish. We tested delivery of phages by different methods (via baths, in phage-coated material, and via oral delivery in feed) to prevent and treat Flavobacterium columnare infections in rainbow trout fry using three phages (FCOV-S1, FCOV-F2, and FCL-2) and their hosts (FCO-S1, FCO-F2, and B185, respectively). Bath treatments given before bacterial infection and at the onset of the disease symptoms were the most efficient way to prevent F. columnare infections in rainbow trout, possibly due to the external nature of the disease. In a flow-through system, the presence of phage-coated plastic sheets delayed the onset of the disease. The oral administration of phages first increased disease progression, although total mortality was lower at the end of the experiment. When analysed for shelf-life, phage titers remained highest when maintained in bacterial culture media and in sterile lake water. Our results show that successful phage therapy treatment in the aquaculture setting requires optimisation of phage delivery methods in vivo.

Phage therapy minimally affects the water microbiota in an Atlantic salmon (Salmo salar) rearing system while still preventing infection

“…The high mortality in untreated germ-free fish, and the fact that we saw no mortality in phage-treated germ-free fish, showed that bacteriophage therapy was successful in increasing survival during infection with F. columnare . The same phage that we used (FCL-2) has also been successfully used earlier in rainbow trout and zebrafish, where elevated survival was observed 38 , 40 . Our findings therefore confirm the potential of using this phage in aquaculture against F. columnare infections.…”

“…This disease is caused by the bacterium Flavobacterium columnare , which infects, amongst others, salmonid fish 4 , 36 , 37 . While antibiotics is the common line of treatment, bacteriophage therapy against F. columnare in aquaculture systems has been demonstrated with promising results 38 – 40 .…”

Phage Delivery Strategies for Biocontrolling Human, Animal, and Plant Bacterial Infections: State of the Art

“…Phage therapy in aquaculture became a greener and safer alternative to the use of antibiotics [ 167 ]. Phage-based pathogen targeting has a variety of uses in both fish and the environment where they are raised [ 168 ].…”

“…Kunttu et al [ 168 ] evaluated the use of phages to prevent and treat infections by Flavobacterium columnare in rainbow trout by using several phage delivery techniques such as via baths, via phage-coated materials, and via oral delivery in fish feed. In this case, the most effective phage therapy procedure consisted in applying phages via bath exposure immediately after the first symptoms of the disease appeared in the fish population.…”

Phage therapy minimally affects the water microbiota in an Atlantic salmon (Salmo salar) rearing system while still preventing infection

“…This disease is caused by the bacterium Flavobacterium columnare, which infects, amongst others, salmonid fish [4,36,37] . While antibiotics is the common line of treatment, bacteriophage therapy against F. columnare in aquaculture systems has been demonstrated with promising results [38][39][40] .…”