Comparative Genomic Analysis of a Novel Vibrio sp. Isolated from an Ulcer Disease Event in Atlantic Salmon (Salmo salar)

Abstract

Ulcer diseases are a recalcitrant issue at Atlantic salmon (Salmo salar) aquaculture cage-sites across the North Atlantic region. Classical ulcerative outbreaks (also called winter ulcer disease) refer to a skin infection caused by Moritella viscosa. However, several bacterial species are frequently isolated from ulcer disease events, and it is unclear if other undescribed pathogens are implicated in ulcer disease in Atlantic salmon. Although different polyvalent vaccines are used against M. viscosa, ulcerative outbreaks are continuously reported in Atlantic salmon in Canada. This study analyzed the phenotypical and genomic characteristics of Vibrio sp. J383 isolated from internal organs of vaccinated farmed Atlantic salmon displaying clinical signs of ulcer disease. Infection assays conducted on vaccinated farmed Atlantic salmon and revealed that Vibrio sp. J383 causes a low level of mortalities when administered intracelomic at doses ranging from 107–108 CFU/dose. Vibrio sp. J383 persisted in the blood of infected fish for at least 8 weeks at 10 and 12 °C. Clinical signs of this disease were greatest 12 °C, but no mortality and bacteremia were observed at 16 °C. The Vibrio sp. J383 genome (5,902,734 bp) has two chromosomes of 3,633,265 bp and 2,068,312 bp, respectively, and one large plasmid of 201,166 bp. Phylogenetic and comparative analyses indicated that Vibrio sp. J383 is related to V. splendidus, with 93% identity. Furthermore, the phenotypic analysis showed that there were significant differences between Vibrio sp. J383 and other Vibrio spp, suggesting J383 is a novel Vibrio species adapted to cold temperatures.

Haemato-Immunological Response of Immunized Atlantic Salmon (Salmo salar) to Moritella viscosa Challenge and Antigens

“…The high survival percentage showed an appropriate immune response of infected fish and confirmed the effectiveness of the ALPHA JECT micro IV vaccine in protecting Atlantic salmon from M. viscosa challenge ( Figure 1 ). The virulence of this M. viscosa strain has been previously verified in Atlantic salmon [ 8 ]. This result was expected since Norwegian strains are used as a vaccine component, such as the M. viscosa type strain used in this study.…”

“…Vaccinated farmed Atlantic salmon (~350 ± 50 g) provided by Cook aquaculture industry were held at the Ocean Sciences Center (Memorial University of Newfoundland). Fish were kept and fed according to the standard protocols [ 8 ], and ethical procedures #18-01-JS, #18-03-JS, and biohazard license L-01 were implemented for the study.…”

“…The Atlantic salmon industry attempts to prevent or control bacterial outbreaks using vaccines [ 6 ]. Although vaccination is an effective management strategy that decreases disease outbreaks and minimizes the use of antibiotics in the aquaculture industry [ 7 ], ulcerative disease is frequently reported in vaccinated Atlantic salmon in eastern Canada [ 8 ]. To develop effective vaccines, an in-depth understanding of the immune response in the target species after immunization is required.…”