Publications by authors named "I Dalsgaard"

95 Publications

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

Microorganisms 2021 Apr 30;9(5). Epub 2021 Apr 30.

Unit for Fish and Shellfish Diseases, National Institute of Aquatic Resources, Technical University of Denmark, 2800 Kongens Lyngby, Denmark.

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). Subsequently, bacteria-challenged eyed eggs were exposed to phages to evaluate their effects in controlling the bacterial population. Culture-based methods were used to enumerate the number of bacteria and/or phages associated with eyed eggs and in the surrounding environment. The results of the study showed that, with our infection model, it was possible to re-isolate associated with eyed eggs after the infection procedure, without affecting the survival of the eggs in the short term. However, this was not possible for , as this bacterium grows at higher temperatures than the ones recommended for incubation of rainbow trout eyed eggs. Bacteriophages do not appear to negatively affect the survival of rainbow trout eyed eggs and they do not seem to strongly adhere to the surface of eyed eggs either. Finally, the results demonstrated a strong potential for short term (24 h) phage control of . However, further studies are needed to explore if phage control can be maintained for a longer period and to further elucidate the mechanisms of interactions between Flavobacteria and their phages in association with fish eggs.
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http://dx.doi.org/10.3390/microorganisms9050971DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8146780PMC
April 2021

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

Front Microbiol 2021 8;12:628309. Epub 2021 Mar 8.

Unit for Fish and Shellfish Diseases, National Institute of Aquatic Resources, Technical University of Denmark, Kgs. Lyngby, Denmark.

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 (1.6 × 10 PFU g) or by irreversible immobilization (8.3 × 10 PFU g), using the corona discharge technology (Fixed Phage Ltd.). The fish showed normal growth for every group and no mortality was observed prior to infection as well as in control groups during the infection. Constant detection of phages in the intestine (∼10 PFU mg) and more sporadic occurrence in kidney, spleen, and brain was observed. When fish were exposed to , no significant effect on fish survival, nor a direct impact on the number of phages in the sampled organs, were detected. Similarly, no significant increase in fish survival was detected when phages were delivered by bath (1 and 2 bath: ∼10 PFU ml; 3 bath: ∼10 PFU ml). However, when phages FpV4 and FPSV-D22 (1.7 × 10 PFU fish) were administered by intraperitoneal injection 3 days after the bacterial challenge, the final percent survival observed in the group injected with bacteriophages FpV4 and FPSV-D22 (80.0%) was significantly higher than in the control group (56.7%). The work demonstrates the delivery of phages to fish organs by oral administration, but also suggests that higher phage dosages than the tested ones may be needed on feed pellets to offer fish an adequate protection against infections.
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http://dx.doi.org/10.3389/fmicb.2021.628309DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7983945PMC
March 2021

A Major QTL for Resistance to in Rainbow Trout.

Front Genet 2020 29;11:607558. Epub 2020 Dec 29.

Laboratory of Aquatic Pathobiology, Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.

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 1.5 × 10 cfu/ml and observed for 14 days. Disease signs appeared 3 days post exposure (dpe) whereafter mortality progressed exponentially until 6 dpe reaching a total mortality of 55% within 11 days. DNA was sampled from all fish - including survivors - and analyzed on a 57 k Affymetrix SNP platform whereby it was shown that disease resistance was associated with a major QTL on chromosome 21 (Omy 21). Gene expression analyses showed that diseased fish activated genes associated with innate and adaptive immune responses. The possible genes associated with resistance are discussed.
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http://dx.doi.org/10.3389/fgene.2020.607558DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7802751PMC
December 2020

Analysis of 44 Vibrio anguillarum genomes reveals high genetic diversity.

PeerJ 2020 3;8:e10451. Epub 2020 Dec 3.

National Institute of Aquatic Resources Technical University of Denmark, Kongens Lyngby, Denmark.

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. Consequently, the aim of the present investigation was to sequence and to characterize a collection of 44 strains obtained primarily from vibriosis outbreaks in Danish rainbow trout. The strains were sequenced, de novo assembled, and the genomes examined for the presence of plasmids, virulence, and acquired antibiotic resistance genes. To investigate the phylogeny, single nucleotide polymorphisms were identified, and the pan-genome was calculated. All strains carried encoding tetracycline resistance, and 36 strains also contained for increased fluoroquinolone/quinolone resistance. But interestingly, all strains were phenotypic sensitive to both oxytetracycline and oxolinic acid. Almost all serotype O1 strains contained a pJM1-like plasmid and nine serotype O2A strains carried the plasmid p15. The distribution of virulence genes was rather similar across the strains, although evident variance among serotypes was observed. Most significant, almost all serotype O2 and O3 strains, as well as the serotype O1 strain without a pJM1-like plasmid, carried genes encoding piscibactin biosynthesis. Hence supporting the hypothesis, that piscibactin plays a crucial role in virulence for pathogenic strains lacking the anguibactin system. The phylogenetic analysis and pan-genome calculations revealed great diversity within . Serotype O1 strains were in general very similar, whereas considerable variation was found among serotype O2A strains. The great diversity within the serotype O2A genomes is most likely the reason why vaccines provide good protection from some strains, but not from others. Hopefully, the new genomic data and knowledge provided in this study might help develop an optimized vaccine against in the future to reduce the use of antibiotics, minimize economic losses and improve the welfare of the fish.
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http://dx.doi.org/10.7717/peerj.10451DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7719292PMC
December 2020

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

Fish Shellfish Immunol 2020 Nov 11;106:441-450. Epub 2020 Aug 11.

Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C., Denmark.

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. Cumulative mortality reached 42% at 12 days post challenge (dpc) after which no disease signs were recorded. All fish were sampled for DNA-typing (50 k SNP chip, Affymetrix®) throughout the course of infection when they showed clinical signs of disease (susceptible fish) or at day 21 when fish showed no clinical signs of disease (survivors - resistant fish). Genome-wide association analyses of 1027 trout applying single nucleotide polymorphisms (SNPs) as markers revealed an association between traits (susceptible/resistant) and certain regions of the trout genome. It was indicated that multiple genes are involved in rainbow trout resistance towards ERM whereby it is considered a polygenic trait. A corresponding trout group was kept as non-exposed controls and a comparative expression analysis of central innate and adaptive immune genes in gills, spleen and liver was performed for three fish groups: 1) moribund trout exhibiting clinical signs 7 dpc (CS), 2) exposed fish without clinical signs at the same sampling point (NCS) and 3) surviving fish at 21 dpc (survivors). Immune genes encoding inflammatory cytokines (IL-1β, IL-2A, IL-6A, IL-8, IL-10A, IL-12, IL-17A/F2A, IL-17C1, IL-17C2, IL-22, IFNγ, TNFα), acute phase reactants (SAA, C3, cathelicidins, lysozyme) were expressed differently in CS and NCS fish. Correlation (negative or positive) between expression of genes and bacterial load suggested involvement of immune genes in protection. Down-regulation of adaptive immune genes including IgDm, IgDs, IgT and TCR-β was seen primarily in CS and NCS fish whereas survivors showed up-regulation of effector molecule genes such as cathelicidins, complement and lysozyme suggesting their role in clearing the infection. In conclusion, SNP analyses indicated that ERM resistance in rainbow trout is a multi-locus trait. The gene expression in surviving fish suggested that several immune genes are associated with the trait conferring resistance.
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http://dx.doi.org/10.1016/j.fsi.2020.07.023DOI Listing
November 2020
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