Isolation and characterization of novel Yersinia ruckeri bacteriophages for potential use in aquaculture

Yersiniosis, caused by Yersinia ruckeri, poses a major threat to aquaculture, particularly in rainbow trout (Oncorhynchus mykiss). This study aimed to isolate, characterize, and evaluate the therapeutic potential of two novel Y. ruckeri-specific bacteriophages, named YP3 and YP10S2S2. Their genomes consisted of double-stranded DNA (dsDNA), with sizes of 36,990 bp for YP3 and 56,579 bp for YP10S2. Phylogenomic analysis classified YP10S2 within the family Drexlerviridae, though its genus and species remain unidentified, while YP3 was placed in the class Caudoviricetes but lacked further taxonomic resolution. Thermal and pH stability tests indicated optimal viability at temperatures up to 25 °C and pH 4–10. in vitro assays demonstrated high adsorption efficiency, short latent periods, and strong lytic activity. Cytotoxicity assays on EPC cells revealed no adverse effects, confirming phage safety. Fish challenge experiment revealed that oral administration of a phage-supplemented diet provided 70 % protection, outperforming intraperitoneal injection (56 %), highlighting oral phage therapy as a more effective disease control strategy. These results suggest that YP3 and YP10S2 are promising candidates for phage therapy in aquaculture due to their specificity, stability, and effectiveness against Y. ruckeri, offering a viable alternative to antibiotics for treating bacterial diseases in fish.