Isolation and Characterisation of Yersinia ruckeri Bacteriophages from Selected Fish Sites in Norway

Abstract

There has been an increase of yersiniosis in Norwegian salmonid production in both freshwater and seawater stages in recent years. The disease is characterised by septicaemia and may cause high mortalities in fry. Antibiotics and vaccines are used for prevention and control of outbreaks. In this thesis we investigate the presence of Y. ruckeri bacteriophages in fish sites with a known previous outbreak of yersiniosis. Five water samples were collected from two different freshwater fish farming sites in Norway and used as sources for bacteriophages. A Y. ruckeri serotype O1 isolate, representing the serotype isolated from salmon with yersiniosis in Norway, was used to screen and propagate the phages. A total of 66 plaques were harvested following the initial screening. All of the water samples were represented with positive results. Out of the 66 isolates, 36 phages were verified with a culture lysis and a plaque formation test. 6 of the most potent isolates in terms of bacteriolysis were selected for further characterisation. Unfortunately, the NMBU got closed due to the Coronavirus outbreak and so the characterisation part of this work could not be completed. The results of this study show that bacteriophages against Y. ruckeri are present and can easily be isolated and utilized as supplements in the treatment or control of yersiniosis. Follow-up studies to characterise them and establish their host range should be done as a next step.