Dataset Information

Efficacy of a polyvalent immersion vaccine against Flavobacterium psychrophilum and evaluation of immune response to vaccination in rainbow trout fry (Onchorynchus mykiss L.).

ABSTRACT: Rainbow trout fry syndrome (RTFS) is a disease caused by the Gram-negative bacterium Flavobacterium psychrophilum, responsible for significant economic losses in salmonid aquaculture worldwide. The diversity of F. psychrophilum isolates and the inherent difficulties in vaccinating juvenile fish has hampered the development of a vaccine for RTFS. Disease episodes tend to occur between 10-14 °C with necrotic lesions often seen on the skin surrounding the dorsal fin and tail. At present no commercial vaccines are available for RTFS in the UK, leaving antibiotics as the only course of action to control disease outbreaks. The current work was performed as a pilot study to assess the efficacy of a polyvalent, whole cell vaccine containing formalin-inactivated F. psychrophilum, to induce protective immunity in rainbow trout fry. Duplicate groups of 30 trout (5 g) were immersed in 1 L of the vaccine for 30 s. Samples were taken 4 h, day 2 and 7 post-vaccination (pv) of skin mucus, tissues for histology and gene expression analysis; serum and histology samples were taken 6 weeks pv. A booster vaccination was given at 315 degree days (dd) also by immersion. Challenge was by immersion with a heterologous isolate of F. psychrophilum 630 dd post primary vaccination. The vaccine provided significant protection to the trout fry with a RPS of 84% (p < 0.0001). Detection of increased numbers of IgT positive cells in systemic organs, up-regulation of IgT expression in hind-gut and an increase in total IgT in serum was observed in vaccinated fish; however a functional role of IgT in the observed protection remains to be demonstrated.

SUBMITTER: Hoare R

PROVIDER: S-EPMC5563058 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature

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Efficacy of a polyvalent immersion vaccine against Flavobacterium psychrophilum and evaluation of immune response to vaccination in rainbow trout fry (Onchorynchus mykiss L.).

Hoare R R Ngo T P H TPH Bartie K L KL Adams A A

Veterinary research 20170818 1

Rainbow trout fry syndrome (RTFS) is a disease caused by the Gram-negative bacterium Flavobacterium psychrophilum, responsible for significant economic losses in salmonid aquaculture worldwide. The diversity of F. psychrophilum isolates and the inherent difficulties in vaccinating juvenile fish has hampered the development of a vaccine for RTFS. Disease episodes tend to occur between 10-14 °C with necrotic lesions often seen on the skin surrounding the dorsal fin and tail. At present no commerci ...[more]

PMID: 28821298

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Project description:Flavobacterium psychrophilum is the causative agent of bacterial cold-water disease in salmonids and rainbow trout fry syndrome. This pathogen has attained a global presence and can spread both horizontally and vertically. However, it was not documented in Korea before September 2018. In this study, the objectives were to characterize Flavobacterium psychrophilum strain FPRT1, isolated from diseased rainbow trout genotypically and phenotypically. We also conducted various investigations to better understand its impact and assess potential control measures. We acquired fifty rainbow trout (approximately 70 g in weight) and transferred them to a laboratory aquarium. During the initial acclimation period, we observed mortality and examined affected fish for clinical signs. We isolated the bacterium from the spleen of infected rainbow trout using tryptone yeast extract salts agar supplemented with glucose, naming this FPRT1. Antibiotic susceptibility testing was carried out, and from the result, we selected enrofloxacin to administer to the trout orally to reduce mortality. To evaluate pathogenicity, we exposed the trout to FPRT1 at different water temperatures (8, 15, and 22 °C). Genomic analysis was conducted to identify the serotype and relatedness of FPRT1 to European strains. Affected fish displayed clinical signs, such as ulcerative lesions in the mandible, anemia with pale gills, exophthalmia, and increased mucus secretion. Internal symptoms included pale liver and enlarged spleen. FPRT1 was susceptible to erythromycin, enrofloxacin, florfenicol, oxytetracycline, and gentamicin, but resistant to oxolinic acid and sulfamethoxazole/trimethoprim. Oral administration of enrofloxacin resulted in a decrease in mortality from 28% to 6%. Pathogenicity tests revealed varying mortality rates due to FPRT1 at different temperatures. The highest rates were observed at 8 °C (ranging from 43% to 100%) for both intraperitoneal and intramuscular injections, and lower rates occurred at 22 °C (ranging from 0% to 30%), with intramuscular injections displaying higher susceptibility. Genomic analysis identified FPRT1 as serotype 2 and indicated its close genetic relationship with European strains based on the core genome and dispensable genome. The substantial genomic similarity between our strain and European strains suggests the possibility of bacterial spread through the importation of fertilized eggs from Europe. In conclusion, this study highlights the introduction of the previously undocumented pathogen (F. psychrophilum) into Korean rainbow trout populations. The detection of this pathogen and its pathogenicity assessment is not only important for understanding its impact on local aquaculture but also for establishing surveillance and control measures to prevent further transmission and outbreaks in the region.

Project description: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 Flavobacterium psychrophilum and investigated the effects of antibiotics (florfenicol) and phage therapies on the gut microbiota of healthy and infected rainbow trout fry (1-2 g). Florfenicol-coated feed was administered for 10 days, starting two days after the infection procedure. A two-component mix of phage targeting F. psychrophilum (FpV4 and FPSV-D22) was continuously delivered by feed with a prophylactic period of 12 days. Samples of the distal intestine were collected over time (day -1 and 1, 8, and 33 days post-infection) and analyzed by community analysis targeting the 16S rRNA gene (V3-V4 region). Results showed the dysbiosis effect caused both by the infection and by florfenicol administration. Shifts in the overall composition were detected by β-diversity analysis, and changes in specific populations were observed during taxonomic mapping. Measures of α-diversity were only affected in infected fish (large variation observed 1 and 8 dpi). These community alterations disappeared again when fish recovered from the infection and the antibiotic treatment was terminated (33 dpi). Interestingly, phage addition altered the microbiota of the fish independently of the presence of their target bacterium. The overall gut bacterial community in fish fed phage-treated feed was different from the controls at each time point as revealed by β-diversity analysis. However, it was not possible to identify specific bacterial populations responsible for these changes except for an increase of lactic acid bacteria 33 dpi. Overall, the results indicate that the administered phages might affect the complex network of phage-bacteria interactions in the fish gut. Nevertheless, we did not observe negative effects on fish health or growth, and further studies should be directed in understanding if these changes are beneficial or not for the fish health with an additional focus on the host immune response.

Dataset Information

Efficacy of a polyvalent immersion vaccine against Flavobacterium psychrophilum and evaluation of immune response to vaccination in rainbow trout fry (Onchorynchus mykiss L.).

Publications

Efficacy of a polyvalent immersion vaccine against Flavobacterium psychrophilum and evaluation of immune response to vaccination in rainbow trout fry (Onchorynchus mykiss L.).

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