ARS | Publication request: Characterisation of a serotype O1 Yersinia ruckeri isolate from the Isle of Man: further evidence that O antigen serotype is not a reliable indicator of virulence

Submitted to: European Association of Fish Pathologists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 14, 2011
Publication Date: June 1, 2011
Citation: Verner-Jeffreys, D.W., Haig, S.J., Welch, T.J., Pond, M.J., Stone, D., Davies, R., Gardner, R. 2011. Characterisation of a serotype O1 Yersinia ruckeri isolate from the Isle of Man: further evidence that O antigen serotype is not a reliable indicator of virulence. European Association of Fish Pathologists. 31(3):86-91.

Interpretive Summary: The Isle of Man is an island off the coast of Great Britain that has a significant rainbow trout farming industry. Until recently, the Isle of Man has been free of Yersinia ruckeri the causative agent of Enteric Redmouth Disease. Here, we report the isolation and characterization of the first Yersinia ruckeri strain from a trout aquaculture facility at the Isle of Man. While the isolate was similar phenotypically to the Y. ruckeri isolates which have been the cause of ERM disease in Europe, the UK and the US, genetic characterization of this isolate demonstrated that this strain is distinct from the strains currently circulating in Europe and the mainland UK. Serum resistance and fish challenge studies suggest that this strain is not highly virulent and thus likely poses less of a risk to salmonids than typical ERM-causing isolates. Vigilant screening for virulent Y. ruckeri isolates has become increasingly important as this pathogen has recently reemerged in the Southwestern US, the UK and in Europe.

Technical Abstract: As part of a routine disease surveillance exercise, a culture of the Gram negative bacterial pathogen Yersinia ruckeri was obtained from one of 150 largely asymptomatic rainbow trout from a farm on the Isle of Man, an island off the North West coast of Great Britain. This is the first reported isolation of Y. ruckeri from the Isle of Man. The isolate was phenotypically and serologically indistinguishable from serotype O1 Y. ruckeri isolates, which have been the cause of the disease enteric redmouth (ERM) in Europe, the UK and the US for more than 30 years. However, the isolate was relatively avirulent, when tested by bath immersion challenge, in rainbow trout and Atlantic salmon, compared to a positive control ERM disease-causing rainbow trout isolate. Detailed molecular subtyping of the isolate using Pulsed Field Gel Electrophoresis (PFGE) also showed the isolate had a different pulsotype to the isolates known to typically circulate in Europe and the mainland UK. Overall, the results support the suggestion that the O1 serogroup contains a heterogeneous assembly of types with respect to pathogenicity and host.