Biological control of Aeromonas salmonicida infection in juvenile Senegalese sole (Solea senegalensis) with Phage AS-A

Abstract

One of the major sources of financial loss for the fish farming industry is the occurrence of infections by pathogenic bacteria, especially multidrug-resistant variants. This problem is most prominent during the early stages of fish development and is difficult to address with traditional antibiotic treatment or vaccination. In this way, alternative environmentally-friendly biological strategies to control bacterial infections need to be implemented. Under this scenario, phage therapy appears as a useful and flexible tool for the inactivation of bacterial pathogens in aquaculture. The aim of this study was to test the efficacy of phage therapy to inactivate Aeromonas salmonicida, the causative agent of furunculosis, a fish disease characterized by high mortality and morbidity. In order to achieve this goal, a new phage was isolated, characterized and tested in artificially-infected Solea senegalensis juveniles and in batch bacterial cultures. Results showed that after 6h of treatment the phage inhibited the growth of A. salmonicida both in batch cultures and seawater in the presence of fish juveniles (≈4 and 2.5LogPFUmL−1, respectively). After 72h, fish juveniles treated with phages after exposure to A. salmonicida showed no mortality, contrarily to fishes that were only exposed to the bacterium, which presented a mortality of 36%. This result indicated that phage treatment was effective. In general, a limited regrowth of resistant cells and absence of lysogeny conversion were observed. No significant impact of phage inoculation on natural bacterial communities of aquaculture water was detected. However, the bacterial community associated with fish intestinal tract was moderately affected by the addition of the phage. Interestingly, the differences were not significant when the phage was added in the presence of the host bacteria. Taking this into account, this study provides evidences that the tested phage can be effective and safe against furunculosis during the production of juvenile fish.Statement of relevanceA major source of financial loss for the fish-farming industry is the occurrence of bacterial infections. This problem is most prominent in early stages of fish development, and is difficult to address with antibiotics/vaccination. Alternative environmentally-friendly strategies to control bacterial infections are needed. This study indicates that phages can be effective and safe against furunculosis during fish juvenile production.