Validation of a QTL associated with resistance to Vibrio anguillarum in rainbow trout (Oncorhynchus mykiss).

Vibriosis is a bacterial disease in fish caused by the Gram negative bacterium Vibrio anguillarum with severe impact on rainbow trout (Oncorhynchus mykiss) farming. Sustainable control methods should be developed and we here show that marker assisted selective breeding of fish naturally resistant to the disease is feasible. We have validated the use of a single nucleotide polymorphism (SNP) marker SNP AX-89,945,921 (QTL on chromosome 21).

Fast and accurate identification by MALDI-TOF of the zoonotic serovar E of Vibrio vulnificus linked to eel culture.

Vibrio vulnificus is a zoonotic pathogen that can cause death by septicaemia in farmed fish (mainly eels) and humans. The zoonotic strains that have been isolated from diseased eels and humans after eel handling belong to clade E (or serovar E (SerE)), a clonal complex within the pathovar (pv.) piscis.

: Response of Vaccinated Large Rainbow Trout to Different Strains.

Background: Although is recognized as the causative pathogen of rainbow trout fry syndrome (RTFS), often resulting in high fry mortality, it is also responsible for bacterial cold water disease (BCWD) in large and older rainbow trout (). These older fish do not experience high mortality, but sustain, through the shedding of bacteria, a constant infection pressure at farm level, which exposes fry to an unnecessary infection risk. We have produced and assessed the immunogenicity of an experimental injection BCWD vaccine, which may be used to decrease the shedding of bacteria from older fish.

Modulation of gut microbiota, blood metabolites, and disease resistance by dietary β-glucan in rainbow trout (Oncorhynchus mykiss).

Background: Prebiotics are known to have a positive impact on fish health and growth rate, and β-glucans are among the most used prebiotics on the market. In this study, rainbow trout (Oncorhynchus mykiss) were treated with a β-1,3;1,6-glucan dietary supplement (at a dose of 0 g, 1 g, 10 g, and 50 g β-glucan per kg of feed). After 6 weeks, the effect of the β-glucan was evaluated by determining the changes in the microbiota and the blood serum metabolites in the fish.

Antigenic variability of Vibrio anguillarum serotype O2a: A hurdle for vaccine efficacy against vibriosis in rainbow trout (Oncorhynchus mykiss).

Despite vaccination, outbreaks of vibriosis still occur in sea-reared rainbow trout in Denmark. Vibriosis outbreaks are caused mainly by V. anguillarum serotypes O1 and O2a, and bacterins of both serotypes are included in the commonly used vaccine against this disease in Danish aquaculture.

Reversible mutations in gliding motility and virulence genes: A flexible and efficient phage defence mechanism in Flavobacterium psychrophilum.

Flavobacteria are among the most important pathogens in freshwater salmonid aquaculture worldwide. Due to concerns regarding development of antibiotic resistance, phage therapy has been proposed as a solution to decrease pathogen load. However, application of phages is challenged by the development of phage resistance, and knowledge of the mechanisms and implications of phage resistance is therefore required.

The Gut Microbiota of Healthy and -Infected Rainbow Trout Fry Is Shaped by Antibiotics and Phage Therapies.

In the aquaculture sector, there is an increased interest in developing environmentally friendly alternatives to antibiotics in the treatment and prevention of bacterial infections. This requires an understanding of the effects of different treatments on the fish microbiota as a measure for improving the fish health status. In this study, we focused on the freshwater pathogen and investigated the effects of antibiotics (florfenicol) and phage therapies on the gut microbiota of healthy and infected rainbow trout fry (1-2 g).

Whole-genome association study searching for QTL for Aeromonas salmonicida resistance in rainbow trout.

Aeromonas salmonicida subsp. salmonicida, the causative agent of furunculosis, has extensive negative effects on wild and farmed salmonids worldwide. Vaccination induces some protection under certain conditions but disease outbreaks occur even in vaccinated fish.

Comparative Genomic Analyses of Isolates Reveals New Putative Genetic Determinants of Virulence Traits.

The fish pathogen is currently one of the main pathogenic bacteria hampering the productivity of salmonid farming worldwide. Although putative virulence determinants have been identified, the genetic basis for variation in virulence of is not fully understood. In this study, we analyzed whole-genome sequences of a collection of 25 isolates from Baltic Sea countries and compared genomic information with a previous determination of their virulence in juvenile rainbow trout.

Immersion vaccines against Yersinia ruckeri infection in rainbow trout: Comparative effects of strain differences.

The protective effects of autogenous and commercial ERM immersion vaccines (bacterins based on Yersinia ruckeri, serotype O1, biotypes 1 and 2) for rainbow trout (Oncorhynchus mykiss) were compared in order to evaluate whether the use of local pathogen strains for immunization can improve protection. In addition, the effect of the bacterin concentration was established for the commercial product. Following sublethal challenge of vaccinated and non-vaccinated control fish with live bacteria, we followed the bacterial count in the fish (gills, liver and spleen).

Genome-informed approach to identify genetic determinants of Flavobacterium psychrophilum phage susceptibility.

The fish pathogen Flavobacterium psychrophilum infects farmed salmonids worldwide, and application of bacteriophages has been suggested for controlling disease outbreaks in aquaculture. Successful application of phages requires detailed knowledge about the variability in phage susceptibility of the host communities. In this study, we analysed the genetic diversity of F.

Interactions between Rainbow Trout Eyed Eggs and spp. Using a Bath Challenge Model: Preliminary Evaluation of Bacteriophages as Pathogen Control Agents.

The microbial community surrounding fish eyed eggs can harbor pathogenic bacteria. In this study we focused on rainbow trout () eyed eggs and the potential of bacteriophages against the pathogenic bacteria and . An infection bath method was first established, and the effects of singular phages on fish eggs was assessed (survival of eyed eggs, interaction of phages with eyed eggs).

Phage-Mediated Control of in Aquaculture: Experiments to Compare Delivery Methods.

Phage-based approaches have gained increasing interest as sustainable alternative strategies to antibiotic treatment or as prophylactic measures against disease outbreaks in aquaculture. The potential of three methods (oral, bath, and injection) for delivering a two-component phage mixture to rainbow trout fry for controlling infections and reduce fish mortality was investigated using bacteriophages FpV4 and FPSV-D22. For the oral administration experiment, bacteriophages were applied on feed pellets by spraying (1.

A Major QTL for Resistance to in Rainbow Trout.

Genetic selection of disease resistant fish is a major strategy to improve health, welfare and sustainability in aquaculture. Mapping of single nucleotide polymorphisms (SNP) in the fish genome may be a fruitful tool to define relevant quantitative trait loci (QTL) and we here show its use for characterization of resistant rainbow trout (). Fingerlings were exposed to the pathogen serotype O1 in a solution of 1.

Analysis of 44 Vibrio anguillarum genomes reveals high genetic diversity.

Vibriosis, a hemorrhagic septicemic disease caused by the bacterium , is an important bacterial infection in Danish sea-reared rainbow trout. Despite of vaccination, outbreaks still occur, likely because the vaccine is based on strains from abroad/other hosts than rainbow trout. Information about the genetic diversity of specifically in Danish rainbow trout, is required to investigate this claim.

Immune gene expression and genome-wide association analysis in rainbow trout with different resistance to Yersinia ruckeri infection.

Selective breeding programmes involving marker assisted selection of innately pathogen resistant strains of rainbow trout rely on reliable controlled infection studies, extensive DNA typing of individual fish and recording of expression of relevant genes. We exposed juvenile rainbow trout (6 h bath to 2.6 × 10 CFU mL) to the fish pathogen Yersinia ruckeri serotype O1, biotype 2, eliciting Enteric Red Mouth Disease ERM, and followed the disease progression over 21 days.

Sequence Analysis of Plasmids in Vibrio anguillarum from Different Fish and Locations.

The genetic diversity of Vibrio anguillarum pJM1-like plasmids was investigated. Plasmids were isolated from 18 V. anguillarum serovar O1 strains collected from different geographic locations and fish species.

Protective effect of in-feed specific IgM towards Yersinia ruckeri in rainbow trout.

Tightened regulations and an environmentally friendly approaches in fish production have greatly reduced the use of antibiotics but green solutions are continuously being explored. The use of functional feed may have a potential in the aquaculture sector in securing biomass and minimizing the loss from disease. In the present study, we tested the concept that blood from the fish slaughterhouse can be used for mass purification of specific antibodies which subsequently can be used for feeding fish and thereby confer protection against diseases.

Biogeography of the fish pathogen Aeromonas salmonicida inferred by vapA genotyping.

A recently described typing system based on sequence variation in the virulence array protein (vapA) gene, encoding the A-layer surface protein array, allows unambiguous subtyping of Aeromonas salmonicida. In the present study, we compile A-layer typing results from a total of 675 A. salmonicida isolates, recovered over a 59-year period from 50 different fish species in 26 countries.

Molecular Epidemiology of subsp. Outbreaks in Marine Rainbow Trout Farms Reveals Extensive Horizontal Gene Transfer and High Genetic Diversity.

The marine bacterium subsp. is a pathogen for a variety of marine animals, as well as for humans, and is nowadays considered an emerging pathogen for fish of importance in marine aquaculture. Recent studies have suggested that outbreaks in fish farms are caused by multiclonal populations of this subspecies that exist in the environment.