Multi-Locus Variable number of tandem repeat Analysis (MLVA) of Yersinia ruckeri 2 confirms the existence of host-specificity, geographic endemism and anthropogenic 3 dissemination of virulent clones

Authors: GULLA, SNORRE - Norwegian Veterinary Institute; BARNES, ANDREW - University Of Queensland; Welch, Timothy - Tim; ROMALDE, JESUS - Universidad De Santiago De Compostela; RYDERE, DAVID - Centre For Environment, Fisheries And Aquaculture Science (CEFAS); ORMSBY, MICHAEL - University Of Glasgow; CARSON, JEREMY - University Of Tasmania; LAGESEN, KARIN - Norwegian Veterinary Institute; VERNER-JEFFREYS, DAVID - Centre For Environment, Fisheries And Aquaculture Science (CEFAS); DAVIES, ROBERT - University Of Glasgow; COLQUHOUN, DUNCAN - Norwegian Veterinary Institute

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2018
Publication Date: 8/1/2018
Citation: Gulla, S., Barnes, A.C., Welch, T.J., Romalde, J.L., Rydere, D., Ormsby, M.J., Carson, J., Lagesen, K., Verner-Jeffreys, D.W., Davies, R.L., Colquhoun, D.J. 2018. Multi-Locus Variable number of tandem repeat Analysis (MLVA) of Yersinia ruckeri 2 confirms the existence of host-specificity, geographic endemism and anthropogenic 3 dissemination of virulent clones. Applied and Environmental Microbiology. doi:10.1128/AEM.00730-18.

Interpretive Summary: An assay was developed for high-resolution typing of the fish pathogen, Yersinia ruckeri. The assay is internationally applicable, robust, and provides clear, unambiguous and easily interpreted results. The assay was able to separate Y. ruckeri isolates into geographically linked and/or possibly host specific groups reflecting its potential utility for epidemiological use, selection of strains for vaccine inclusion, and risk assessment. Typing is inexpensive, with a moderate technological requirement, and may be completed within a single working day. As the resulting profiles are readily portable, any strain may rapidly be placed in a global epidemiological context.

Technical Abstract: An MLVA assay was developed for epidemiological study of the internationally important fish pathogen Yersinia ruckeri, which causes yersiniosis or enteric redmouth disease (ERM) in salmonids. The MLVA is based on analysis of ten VNTR loci amplified in two five-plex PCR reactions, followed by capillary electrophoresis. A collection of 484 Y. ruckeri isolates, originating from various biological sources and collected from four continents over seven decades, was examined. MLVA separated the studied population into nine major clonal complexes, and a number of minor clusters and singletons. The major clonal complexes could be associated with host species, geographic origin and serotype. A single large clonal complex of serotype O1 isolates dominating the yersiniosis situation in international rainbow trout farming suggests anthropogenic spread of this clone, possibly related to transport of fish. Moreover, subclustering within this clonal complex indicates putative transmission routes and supports previous reports of biotype shift events. In contrast to the situation in rainbow trout, Y. ruckeri strains associated with disease in Atlantic salmon appear as more or less geographically isolated clonal complexes. A single complex of serotype O1 exclusive to Norway was found to be responsible for almost all major yersiniosis outbreaks in modern Norwegian salmon farming, and site-specific sub-clustering further indicates persistent colonisation of freshwater farms in Norway. Identification of genetically diverse isolates from clinically healthy fish and environmental sources also suggests widespread existence of less virulent or avirulent strains.