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

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