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Gulla S.,Vaxxinova Norway AS Bergen Norway | Lund V.,Nofima Tromso Norway | Kristoffersen A.B.,Norwegian Veterinary Institute Oslo Norway | Sorum H.,Norwegian University of Life Sciences | Colquhoun D.J.,University of Bergen
Journal of Fish Diseases | Year: 2015

Sequence variation in a region of the virulence array protein gene (vapA; A-layer) was assessed in 333 ('typical' and 'atypical') isolates of the fish pathogenic bacterium Aeromonas salmonicida. Resulting similarity dendrograms revealed extensive heterogeneity, with nearly all isolates belonging to either of 14 distinct clusters or A-layer types. All acknowledged A. salmonicida subspecies (except ssp. pectinolytica, from which no vapA sequence could be obtained) were clearly separated, and notably, all isolates phenotypically identified as ssp. salmonicida formed a distinct and exclusive A-layer type. Additionally, an array of un-subspeciated atypical strains formed several equally prominent clusters, demonstrating that the concept of typical/atypical A. salmonicida is inappropriate for describing the high degree of diversity evidently occurring outside ssp. salmonicida. Most representatives assessed in this study were clinical isolates of spatiotemporally diverse origins, and were derived from a variety of hosts. We observed that from several fish species or families, isolates predominantly belonged to certain A-layer types, possibly indicating a need for host-/A-layer type-specific A. salmonicida vaccines. All in all, A-layer typing shows promise as an inexpensive and rapid means of unambiguously distinguishing clinically relevant A. salmonicida subspecies, as well as presently un-subspeciated atypical strains. © 2015 John Wiley & Sons Ltd.


Marana M.H.,Copenhagen University | Skov J.,Copenhagen University | Chettri J.K.,Copenhagen University | Krossoy B.,Vaxxinova Norway AS Bergen Norway | And 3 more authors.
Journal of Fish Diseases | Year: 2016

Rainbow trout, Oncorhynchus mykiss (Walbaum), are able to raise a protective immune response against Aeromonas salmonicida subsp. salmonicida (AS) following injection vaccination with commercial vaccines containing formalin-killed bacteria, but the protection is often suboptimal under Danish mariculture conditions. We elucidated whether protection can be improved by increasing the concentration of antigen (formalin-killed bacteria) in the vaccine. Rainbow trout juveniles were vaccinated by intraperitoneal (i.p.) injection with a bacterin of Aeromonas salmonicida subsp. salmonicida strain 090710-1/23 in combination with Vibrio anguillarum serotypes O1 and O2a supplemented with an oil adjuvant. Three concentrations of AS antigens were applied. Fish were subsequently challenged with the homologous bacterial strain administered by perforation of the tail fin epidermis and 60-s contact with live A. salmonicida bacteria. The infection method proved to be efficient and could differentiate efficacies of different vaccines. It was shown that protection and antibody production in exposed fish were positively correlated to the AS antigen concentration in the vaccine. © 2016 John Wiley & Sons Ltd.

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