Yersinia ruckeri Isolates Recovered from Diseased Atlantic Salmon (Salmo salar) in Scotland Are More Diverse than Those from Rainbow Trout (Oncorhynchus mykiss) and Represent Distinct Subpopulations

Abstract

Yersinia ruckeri is the etiological agent of enteric redmouth (ERM) disease of farmed salmonids. Enteric redmouth disease is traditionally associated with rainbow trout (Oncorhynchus mykiss, Walbaum), but its incidence in Atlantic salmon (Salmo salar) is increasing. Yersinia ruckeri isolates recovered from diseased Atlantic salmon have been poorly characterized, and very little is known about the relationship of the isolates associated with these two species. Phenotypic approaches were used to characterize 109 Y. ruckeri isolates recovered over a 14-year period from infected Atlantic salmon in Scotland; 26 isolates from infected rainbow trout were also characterized. Biotyping, serotyping, and comparison of outer membrane protein profiles identified 19 Y. ruckeri clones associated with Atlantic salmon but only five associated with rainbow trout; none of the Atlantic salmon clones occurred in rainbow trout and vice versa. These findings suggest that distinct subpopulations of Y. ruckeri are associated with each species. A new O serotype (designated O8) was identified in 56 biotype 1 Atlantic salmon isolates and was the most common serotype identified from 2006 to 2011 and in 2014, suggesting an increased prevalence during the time period sampled. Rainbow trout isolates were represented almost exclusively by the same biotype 2, serotype O1 clone that has been responsible for the majority of ERM outbreaks in this species within the United Kingdom since the 1980s. However, the identification of two biotype 2, serotype O8 isolates in rainbow trout suggests that vaccines containing serotypes O1 and O8 should be evaluated in both rainbow trout and Atlantic salmon for application in Scotland. IMPORTANCEVaccination plays an important role in protecting Atlantic salmon against the bacterial pathogen Yersinia ruckeri, but, in recent years, there has been an increasing incidence of vaccine breakdown in salmon. This is largely because current vaccines are aimed at rainbow trout and are based on serotypes specific for this species. A wider range of serotypes is responsible for infection in Atlantic salmon, but very little is known about the diversity of these strains and their relationships to those recovered from rainbow trout. In the present study, we demonstrate that Y. ruckeri isolates recovered from diseased Atlantic salmon in Scotland are more diverse than those from rainbow trout; furthermore, isolates from the two species represent distinct subpopulations. In addition, a new O serotype was identified that is responsible for a significant proportion of the disease in Atlantic salmon. Our findings are likely to have important implications for the development of improved vaccines against Y. ruckeri. The Gram-negative bacterium Yersinia ruckeri is the etiological agent of enteric redmouth (ERM) disease of cultured salmonids and causes significant economic losses to the fish-farming industry. Yersinia ruckeri was first isolated in 1956 from diseased rainbow trout (Oncorhynchus mykiss, Walbaum) in the Hagerman Valle...

Dissecting the immune pathways stimulated following injection vaccination of rainbow trout (Oncorhynchus mykiss) against enteric redmouth disease (ERM)

“…This issue can be resolved by including new isolates in the improved vaccine preparation, as shown with AquaVac(®) RELERA™ that contains both biotypes 1 and 2 of Y. ruckeri and provides better protection [8][9]. Moreover, distinct strains of Y. ruckeri are present in the environment and can evolve with the introduction of susceptible hosts and vaccination of salmonids in aquaculture [10][11]. As the production of global aquaculture continues to increase it is likely that vaccines against other bacterial disease will encounter similar issues and will need the development of improved formulations.…”

Molecular Characterization, Phylogenetic, Expression, and Protective Immunity Analysis of OmpF, a Promising Candidate Immunogen Against Yersinia ruckeri Infection in Channel Catfish

“…Yersinia ruckeri ( Y. ruckeri ) is a Gram-negative rod-shaped enterobacterium and the causative agent of enteric red mouth disease (ERM), one of the most serious septicemic bacterial disease of salmonid fish species ( 1 ). It has been reported that Y. ruckeri has been increasingly widespread and been detected as an important pathogen of salmonid fish in many other countries ( 2 – 6 ) since its isolation in North American ( 7 – 10 ). Apart from salmonids, Y. ruckeri can also infect other non-salmonid fish species including common carp ( 11 ), whitefish ( 12 ), sturgeon ( 13 – 15 ), and channel catfish ( 16 , 17 ).…”

Experimental infection by Yersinia ruckeri O1 biotype 2 induces brain lesions and neurological signs in rainbow trout (Oncorhynchus mykiss)

“…Enteric redmouth (ERM) disease caused by the enterobacterium Yersinia ruckeri is a contagious disease in finfish with cultured salmonid species, including rainbow trout (Oncorhynchus mykiss), being especially susceptible. Among the identified six different serotypes (O1, O2, O3, O5, O7 and O8) of Y. ruckeri, motile strains belonging to serotype O1 (biotype 1) are considered as the most virulent and has been reported as the cause of outbreaks of ERM in cultured salmonids (Barnes, 2011;Furones, Rodgers, & Munn, 1993;Ormsby et al, 2016;Romalde & Toranzo, 1993;Welch et al, 2011). Subsequently, highly virulent non-motile strains of Y. ruckeri serotype O1 (biotype 2) have emerged in Europe (Davies & Frerichs, 1989) and spread worldwide in reoccurring ERM outbreaks in salmonid aquaculture (Arias et al, 2007;Bastardo, Sierralta, Leon, Ravelo, & Romalde, 2011;Huang et al, 2013;McArdle, 2014;Str€ om-Bestor et al, 2010;Wheeler et al, 2009).…”