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Pepi M, Focardi S. Antibiotic-Resistant Bacteria in Aquaculture and Climate Change: A Challenge for Health in the Mediterranean Area. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2021; 18:5723. [PMID: 34073520 PMCID: PMC8198758 DOI: 10.3390/ijerph18115723] [Citation(s) in RCA: 64] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Revised: 05/11/2021] [Accepted: 05/22/2021] [Indexed: 12/30/2022]
Abstract
Aquaculture is the productive activity that will play a crucial role in the challenges of the millennium, such as the need for proteins that support humans and the respect for the environment. Aquaculture is an important economic activity in the Mediterranean basin. A great impact is presented, however, by aquaculture practices as they involve the use of antibiotics for treatment and prophylaxis. As a consequence of the use of antibiotics in aquaculture, antibiotic resistance is induced in the surrounding bacteria in the column water, sediment, and fish-associated bacterial strains. Through horizontal gene transfer, bacteria can diffuse antibiotic-resistance genes and mobile resistance genes further spreading genetic determinants. Once triggered, antibiotic resistance easily spreads among aquatic microbial communities and, from there, can reach human pathogenic bacteria, making vain the use of antibiotics for human health. Climate change claims a significant role in this context, as rising temperatures can affect cell physiology in bacteria in the same way as antibiotics, causing antibiotic resistance to begin with. The Mediterranean Sea represents a 'hot spot' in terms of climate change and aspects of antibiotic resistance in aquaculture in this area can be significantly amplified, thus increasing threats to human health. Practices must be adopted to counteract negative impacts on human health, with a reduction in the use of antibiotics as a pivotal point. In the meantime, it is necessary to act against climate change by reducing anthropogenic impacts, for example by reducing CO2 emissions into the atmosphere. The One Health type approach, which involves the intervention of different skills, such as veterinary, ecology, and medicine in compliance with the principles of sustainability, is necessary and strongly recommended to face these important challenges for human and animal health, and for environmental safety in the Mediterranean area.
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Affiliation(s)
- Milva Pepi
- Stazione Zoologica Anton Dohrn, Fano Marine Centre, Viale Adriatico 1-N, 61032 Fano, Italy;
| | - Silvano Focardi
- Department of Environmental Sciences, Università di Siena, Via Mattioli, 4, 53100 Siena, Italy
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2
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Donati VL, Dalsgaard I, Sundell K, Castillo D, Er-Rafik M, Clark J, Wiklund T, Middelboe M, Madsen L. Phage-Mediated Control of Flavobacterium psychrophilum in Aquaculture: In vivo Experiments to Compare Delivery Methods. Front Microbiol 2021; 12:628309. [PMID: 33763046 PMCID: PMC7983945 DOI: 10.3389/fmicb.2021.628309] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Accepted: 02/15/2021] [Indexed: 12/31/2022] Open
Abstract
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 Flavobacterium psychrophilum 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 × 108 PFU g-1) or by irreversible immobilization (8.3 × 107 PFU g-1), 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 (∼103 PFU mg-1) and more sporadic occurrence in kidney, spleen, and brain was observed. When fish were exposed to F. psychrophilum, 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 (1st and 2nd bath: ∼106 PFU ml-1; 3rd bath: ∼105 PFU ml-1). However, when phages FpV4 and FPSV-D22 (1.7 × 108 PFU fish-1) 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 F. psychrophilum infections.
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Affiliation(s)
- Valentina Laura Donati
- Unit for Fish and Shellfish Diseases, National Institute of Aquatic Resources, Technical University of Denmark, Kgs. Lyngby, Denmark
| | - Inger Dalsgaard
- Unit for Fish and Shellfish Diseases, National Institute of Aquatic Resources, Technical University of Denmark, Kgs. Lyngby, Denmark
| | - Krister Sundell
- Laboratory of Aquatic Pathobiology, Environmental and Marine Biology, Åbo Akademi University, Turku, Finland
| | - Daniel Castillo
- Marine Biological Section, Department of Biology, University of Copenhagen, Helsingør, Denmark
| | - Mériem Er-Rafik
- National Centre for Nano Fabrication and Characterization, Technical University of Denmark, Kgs. Lyngby, Denmark
| | | | - Tom Wiklund
- Laboratory of Aquatic Pathobiology, Environmental and Marine Biology, Åbo Akademi University, Turku, Finland
| | - Mathias Middelboe
- Marine Biological Section, Department of Biology, University of Copenhagen, Helsingør, Denmark
| | - Lone Madsen
- Unit for Fish and Shellfish Diseases, National Institute of Aquatic Resources, Technical University of Denmark, Kgs. Lyngby, Denmark
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3
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High Genetic Diversity in Flavobacterium psychrophilum Isolates from Healthy Rainbow Trout (Oncorhynchus mykiss) Farmed in the Same Watershed, Revealed by Two Typing Methods. Appl Environ Microbiol 2021; 87:AEM.01398-20. [PMID: 33158894 DOI: 10.1128/aem.01398-20] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Accepted: 10/28/2020] [Indexed: 12/16/2022] Open
Abstract
Flavobacterium psychrophilum affects salmonid health worldwide and causes economic losses. The genetic diversity of the pathogen must be considered to develop control methods. However, previous studies have reported both high and low levels of genetic diversity. The present longitudinal study aimed at assessing the genetic diversity of F. psychrophilum at a small temporal and geographic scale. Four farms located on the same watershed in France were studied. Rainbow trout (Oncorhynchus mykiss) batches were monitored, and apparently healthy individuals were sampled over 1 year. A total of 288 isolates were recovered from fish organs (gills and spleen) and eggs. Pulsed field gel electrophoresis revealed high genetic diversity. Multilocus sequence typing performed on a selection of 31 isolates provided congruent results, as follows: 18 sequence types (STs) were found, of which 13 were novel. The mean gene diversity (H = 0.8413) was much higher than that previously reported for this host species, although the sampling was restricted to a single watershed and 1 year. Seven isolates out of 31 were assigned to clonal complex ST10 (CC-ST10), which is the predominant clonal complex in the main salmonid production areas. A split decomposition tree reflected a panmictic population. This finding is important for aquaculture veterinarians in their diagnostic procedure, as the choice of adequate antibiotic treatment is conditioned by the correct identification of the causative agent. Furthermore, this study expands our knowledge on genetic diversity required for the development of an effective vaccine against F. psychrophilum IMPORTANCE The bacterium Flavobacterium psychrophilum is a serious pathogen in many fish species, especially salmonids, that is responsible for considerable economic losses worldwide. In order to treat infections and to develop vaccines, the genetic diversity of this bacterium needs to be known. We assessed the genetic diversity of F. psychrophilum isolates from apparently healthy rainbow trout raised in several fish farms in the same watershed in France. Two different genotyping methods revealed high diversity. The majority of isolates were unrelated to clonal complex sequence type 10 (CC-ST10), the clonal complex that is predominant worldwide and associated with disease in rainbow trout. In addition, we found 13 novel sequence types. These results suggest that a diverse subpopulation of F. psychrophilum may be harbored by rainbow trout.
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Jarau M, MacInnes JI, Lumsden JS. Erythromycin and florfenicol treatment of rainbow trout Oncorhynchus mykiss (Walbaum) experimentally infected with Flavobacterium psychrophilum. JOURNAL OF FISH DISEASES 2019; 42:325-334. [PMID: 30632170 DOI: 10.1111/jfd.12944] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2018] [Revised: 09/06/2018] [Accepted: 09/07/2018] [Indexed: 06/09/2023]
Abstract
Flavobacterium psychrophilum is responsible for significant economic losses in rainbow trout aquaculture. Antimicrobial treatment remains the primary means of control; however, there are limited choices available for use. The objectives of the study were therefore to determine the minimum inhibitory concentrations for erythromycin and florfenicol in selected F. psychrophilum isolates and to evaluate their clinical treatment efficacy in experimentally infected rainbow trout. All isolates tested had moderate susceptibility to florfenicol and erythromycin except one isolate, which had low susceptibility to erythromycin. Two isolates (one with moderate and one with low susceptibility to erythromycin) were used in an experimental infection trial. Rainbow trout juveniles were injected intraperitoneally with 108 cfu/fish and after mortality had begun, fish were given erythromycin- and florfenicol-medicated feed at a rate of 75 mg kg- 1 day- 1 and 10 mg kg- 1 day- 1 fish body weight, respectively, for 10 consecutive days. The splenic F. psychrophilum load was determined using an rpoC quantitative PCR throughout the 30-day trial. Relative to antibiotic-free controls, erythromycin treatment significantly (p < 0.05) reduced mortality of rainbow trout juveniles infected with FPG101, even when treatment was initiated after clinical signs developed.
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Affiliation(s)
- Maureen Jarau
- Fish Pathology Laboratory, University of Guelph, Guelph, Ontario, Canada
| | - Janet I MacInnes
- Department of Pathobiology, University of Guelph, Guelph, Ontario, Canada
| | - John S Lumsden
- Fish Pathology Laboratory, University of Guelph, Guelph, Ontario, Canada
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5
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Hoare R, Jung SJ, Ngo TPH, Bartie K, Bailey J, Thompson KD, Adams A. Efficacy and safety of a non-mineral oil adjuvanted injectable vaccine for the protection of Atlantic salmon (Salmo salar L.) against Flavobacterium psychrophilum. FISH & SHELLFISH IMMUNOLOGY 2019; 85:44-51. [PMID: 29017943 DOI: 10.1016/j.fsi.2017.10.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Revised: 10/04/2017] [Accepted: 10/06/2017] [Indexed: 06/07/2023]
Abstract
Flavobacterium psychrophilum is the causative agent of Rainbow Trout Fry Syndrome which has had a major impact on global salmonid aquaculture. Recent outbreaks in Atlantic salmon in Scotland and Chile have added to the need for a vaccine to protect both salmon and trout. At present no licensed vaccines are available in Europe, leaving antibiotics as the only course of action to contain disease outbreaks. Outbreaks generally occur in fry at temperatures between 10 and 15 °C. Recently outbreaks in larger fish have given added impetus to the development of a vaccine which can provide long term protection from this highly heterogeneous pathogen. Most fish injectable vaccines are formulated with oil emulsion adjuvants to induce strong and long lasting immunity, but which are known to cause side effects. Alternative adjuvants are currently sought to minimise these adverse effects. The current study was performed to assess the efficacy of a polyvalent, whole cell vaccine containing formalin-inactivated F. psychrophilum to induce protective immunity in Atlantic salmon. The vaccine was formulated with an adjuvant containing squalene and aluminium hydroxide, and was compared to a vaccine formulated with a traditional oil adjuvant, Montanide ISA 760VG, and a non-adjuvanted vaccine. Duplicate groups of salmon (23.5 ± 6.8 g) were vaccinated with each of the vaccine formulations or phosphate buffered saline by intraperitoneal injection. Fish were challenged by intramuscular injection with F. psychrophilum six weeks post-vaccination to test the efficacy of the vaccines. Cumulative mortality reached 70% in the control salmon, while the groups of salmon that received vaccine had significantly lower mortality than the controls (p = 0.0001), with no significant difference in survival between vaccinated groups. The squalene/alum adjuvant was safe, more readily metabolised by the fish and induced less histopathological changes than the traditional oil adjuvant.
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Affiliation(s)
- R Hoare
- Institute of Aquaculture, University of Stirling, Stirling, UK.
| | - S-J Jung
- Chonnam National University, Yeosu, Republic of Korea
| | - T P H Ngo
- Institute of Aquaculture, University of Stirling, Stirling, UK
| | - K Bartie
- Institute of Aquaculture, University of Stirling, Stirling, UK
| | - J Bailey
- Institute of Aquaculture, University of Stirling, Stirling, UK
| | - K D Thompson
- Moredun Research Institute, Pentland Science Park, Penicuik, UK
| | - A Adams
- Institute of Aquaculture, University of Stirling, Stirling, UK
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6
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Ngo TPH, Smith P, Bartie KL, Thompson KD, Verner-Jeffreys DW, Hoare R, Adams A. Antimicrobial susceptibility of Flavobacterium psychrophilum isolates from the United Kingdom. JOURNAL OF FISH DISEASES 2018; 41:309-320. [PMID: 29064104 DOI: 10.1111/jfd.12730] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Revised: 08/08/2017] [Accepted: 08/11/2017] [Indexed: 06/07/2023]
Abstract
Routine application of antimicrobials is the current treatment of choice for rainbow trout fry syndrome (RTFS) or bacterial coldwater disease (BCWD) caused by Flavobacterium psychrophilum. In this study, the antimicrobial susceptibilities of 133 F. psychrophilum isolates, 118 of which were from the UK, were evaluated by broth microdilution and disc diffusion methods following VET04-A2 and VET03-A guidelines of Clinical and Laboratory Standards Institute (CLSI), respectively. Isolates were categorized as wild type (fully susceptible, WT) or non-wild type (NWT) using normalized resistance interpretation (NRI)-determined cut-off values (COWT ). Broth microdilution testing showed that only 12% of UK isolates were WT to oxolinic acid (MIC COWT ≤ 0.25 mg/L) and 42% were WT for oxytetracycline (MIC COWT ≤ 0.25 mg/L). In contrast, all the isolates tested were WT (MIC COWT ≤ 2 mg/L) for florfenicol, the main antimicrobial for RTFS control in the UK. Disc diffusion-based COWT values were ≥51 mm for 10 μg amoxicillin, ≥44 mm for 30 μg florfenicol, ≥30 mm for 2 μg oxolinic acid and ≥51 mm for 30 μg oxytetracycline. There was a high categorical agreement between the classifications of the isolates by two testing methods for florfenicol (100%), oxytetracycline (93%) and oxolinic acid (99%).
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Affiliation(s)
- T P H Ngo
- Institute of Aquaculture, University of Stirling, Stirling, UK
- Division of Aquacultural Biotechnology, Biotechnology Center of Ho Chi Minh city, Ho Chi Minh city, Vietnam
| | - P Smith
- National University of Ireland, Galway, Ireland
| | - K L Bartie
- Institute of Aquaculture, University of Stirling, Stirling, UK
| | - K D Thompson
- Moredun Research Institute, Pentlands Science Park, Penicuik, UK
| | - D W Verner-Jeffreys
- The Centre for Environment, Fisheries and Aquaculture Science, The Nothe, Weymouth, UK
| | - R Hoare
- Institute of Aquaculture, University of Stirling, Stirling, UK
| | - A Adams
- Institute of Aquaculture, University of Stirling, Stirling, UK
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7
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Abstract
ABSTRACT
Major concerns surround the use of antimicrobial agents in farm-raised fish, including the potential impacts these uses may have on the development of antimicrobial-resistant pathogens in fish and the aquatic environment. Currently, some antimicrobial agents commonly used in aquaculture are only partially effective against select fish pathogens due to the emergence of resistant bacteria. Although reports of ineffectiveness in aquaculture due to resistant pathogens are scarce in the literature, some have reported mass mortalities in
Penaeus monodon
larvae caused by
Vibrio harveyi
resistant to trimethoprim-sulfamethoxazole, chloramphenicol, erythromycin, and streptomycin. Genetic determinants of antimicrobial resistance have been described in aquaculture environments and are commonly found on mobile genetic elements which are recognized as the primary source of antimicrobial resistance for important fish pathogens. Indeed, resistance genes have been found on transferable plasmids and integrons in pathogenic bacterial species in the genera
Aeromonas
,
Yersinia
,
Photobacterium
,
Edwardsiella
, and
Vibrio
. Class 1 integrons and IncA/C plasmids have been widely identified in important fish pathogens (
Aeromonas
spp.,
Yersinia
spp.,
Photobacterium
spp.,
Edwardsiella
spp., and
Vibrio
spp.) and are thought to play a major role in the transmission of antimicrobial resistance determinants in the aquatic environment. The identification of plasmids in terrestrial pathogens (
Salmonella enterica
serotypes,
Escherichia coli
, and others) which have considerable homology to plasmid backbone DNA from aquatic pathogens suggests that the plasmid profiles of fish pathogens are extremely plastic and mobile and constitute a considerable reservoir for antimicrobial resistance genes for pathogens in diverse environments.
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Hoare R, Ngo TPH, Bartie KL, Adams A. Efficacy of a polyvalent immersion vaccine against Flavobacterium psychrophilum and evaluation of immune response to vaccination in rainbow trout fry (Onchorynchus mykiss L.). Vet Res 2017; 48:43. [PMID: 28821298 PMCID: PMC5563058 DOI: 10.1186/s13567-017-0448-z] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Accepted: 07/19/2017] [Indexed: 11/24/2022] Open
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.
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Affiliation(s)
- R Hoare
- Institute of Aquaculture, University of Stirling, Stirling, FK9 4LA, UK.
| | - T P H Ngo
- Institute of Aquaculture, University of Stirling, Stirling, FK9 4LA, UK
| | - K L Bartie
- Institute of Aquaculture, University of Stirling, Stirling, FK9 4LA, UK
| | - A Adams
- Institute of Aquaculture, University of Stirling, Stirling, FK9 4LA, UK
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Ngo TP, Bartie KL, Thompson KD, Verner-Jeffreys DW, Hoare R, Adams A. Genetic and serological diversity of Flavobacterium psychrophilum isolates from salmonids in United Kingdom. Vet Microbiol 2017; 201:216-224. [DOI: 10.1016/j.vetmic.2017.01.032] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 01/26/2017] [Accepted: 01/27/2017] [Indexed: 10/20/2022]
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Miranda CD, Smith P, Rojas R, Contreras-Lynch S, Vega JMA. Antimicrobial Susceptibility of Flavobacterium psychrophilum from Chilean Salmon Farms and Their Epidemiological Cut-Off Values Using Agar Dilution and Disk Diffusion Methods. Front Microbiol 2016; 7:1880. [PMID: 27933043 PMCID: PMC5122587 DOI: 10.3389/fmicb.2016.01880] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2016] [Accepted: 11/09/2016] [Indexed: 11/13/2022] Open
Abstract
Flavobacterium psychrophilum is the most important bacterial pathogen for freshwater farmed salmonids in Chile. The aims of this study were to determine the susceptibility to antimicrobials used in fish farming of Chilean isolates and to calculate their epidemiological cut-off (COWT) values. A number of 125 Chilean isolates of F. psychrophilum were isolated from reared salmonids presenting clinical symptoms indicative of flavobacteriosis and their identities were confirmed by 16S rRNA polymerase chain reaction. Susceptibility to antibacterials was tested on diluted Mueller-Hinton by using an agar dilution MIC method and a disk diffusion method. The COWT values calculated by Normalized Resistance Interpretation (NRI) analysis allow isolates to be categorized either as wild-type fully susceptible (WT) or as manifesting reduced susceptibility (NWT). When MIC data was used, NRI analysis calculated a COWT of ≤0.125, ≤2, and ≤0.5 μg mL-1 for amoxicillin, florfenicol, and oxytetracycline, respectively. For the quinolones, the COWT were ≤1, ≤0.5, and ≤0.125 μg mL-1 for oxolinic acid, flumequine, and enrofloxacin, respectively. The disk diffusion data sets obtained in this work were extremely diverse and were spread over a wide range. For the quinolones there was a close agreement between the frequencies of NWT isolates calculated using MIC and disk data. For oxolinic acid, flumequine, and enrofloxacin the frequencies were 45, 39, and 38% using MIC data, and 42, 41, and 44%, when disk data were used. There was less agreement with the other antimicrobials, because NWT frequencies obtained using MIC and disk data, respectively, were 24 and 10% for amoxicillin, 8 and 2% for florfenicol, and 70 and 64% for oxytetracycline. Considering that the MIC data was more precise than the disk diffusion data, MIC determination would be the preferred method for susceptibility testing for this species and the NWT frequencies derived from the MIC data sets should be considered as the more authoritative. Despite the high frequency of isolates showing full susceptibility to florfenicol, the significant frequencies of isolates exhibiting reduced susceptibility to oxytetracycline and quinolones may result in treatment failures when these agents are used.
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Affiliation(s)
- Claudio D. Miranda
- Laboratorio de Patobiología Acuática, Departamento de Acuicultura, Universidad Católica del NorteCoquimbo, Chile
- Centro AquaPacíficoCoquimbo, Chile
| | - Peter Smith
- Department of Microbiology, School of Natural Sciences, National University of IrelandGalway, Ireland
| | - Rodrigo Rojas
- Laboratorio de Patobiología Acuática, Departamento de Acuicultura, Universidad Católica del NorteCoquimbo, Chile
- Centro AquaPacíficoCoquimbo, Chile
| | | | - J. M. Alonso Vega
- Programa Consorciado Doctorado en Acuicultura, Universidad Católica del NorteCoquimbo, Chile
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Sudheesh PS, Cain KD. Optimization of efficacy of a live attenuated Flavobacterium psychrophilum immersion vaccine. FISH & SHELLFISH IMMUNOLOGY 2016; 56:169-180. [PMID: 27403595 DOI: 10.1016/j.fsi.2016.07.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Revised: 06/16/2016] [Accepted: 07/08/2016] [Indexed: 06/06/2023]
Abstract
This study was aimed at optimizing the efficacy of a recently developed live attenuated immersion vaccine (B.17-ILM) as a promising vaccine against bacterial coldwater disease (BCWD) caused by Flavobacterium psychrophilum in salmonids. Rainbow trout (RBT) fry were vaccinated by immersion, and different parameters affecting vaccination such as fish size, vaccine delivery time, dose, duration of protection, booster regimes and vaccine growth incubation time were optimized. Specific anti-F. psychrophilum immune response was determined by ELISA. Protective efficacy was determined by challenging with a virulent strain of F. psychrophilum (CSF-259-93) and calculating cumulative percent mortality (CPM) and relative percent survival (RPS). All vaccinated fish developed significantly higher levels of serum antibody titers by week 8 when compared to their respective controls. Immersion vaccination for 3, 6 and 30 min produced significant protection with comparable RPS values of 47%, 53% and 52%, respectively. This vaccine provided significant protection for fish as small as 0.5 g with an RPS of 55%; larger fish of 1 g and 2 g yielded slightly higher RPS values of 59% and 60%, respectively. Fish vaccinated with higher vaccine doses of ∼10(10) and 10(8) colony forming units mL(-1) (cfu ml(-1)) were strongly protected out to at least 24 weeks with RPS values up to 70%. Fish vaccinated with lower doses (∼10(6) and 10(5) cfu mL(-1)) had good protection out to 12 weeks, but RPS values dropped to 36% and 34%, respectively by 24 weeks. Vaccine efficacy was optimum when the primary vaccination was followed by a single booster (week 12 challenge RPS = 61%) rather than two boosters (week 12 challenge RPS = 48%). Vaccination without a booster resulted in a lower RPS (13%) indicating the necessity of a single booster vaccination to maximize efficacy. This study presents key findings that demonstrate the efficacy and commercial potential for this live attenuated BCWD vaccine.
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Affiliation(s)
- Ponnerassery S Sudheesh
- Department of Fish and Wildlife Sciences and Aquaculture Research Institute, College of Natural Resources, University of Idaho, Moscow, ID 83844-1136, USA
| | - Kenneth D Cain
- Department of Fish and Wildlife Sciences and Aquaculture Research Institute, College of Natural Resources, University of Idaho, Moscow, ID 83844-1136, USA.
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12
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Gieseker CM, Crosby TC, Mayer TD, Bodeis SM, Stine CB. Development of Similar Broth Microdilution Methods to Determine the Antimicrobial Susceptibility of Flavobacterium columnare and F. psychrophilum. JOURNAL OF AQUATIC ANIMAL HEALTH 2016; 28:27-38. [PMID: 26949840 DOI: 10.1080/08997659.2015.1105878] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Flavobacterium columnare and F. psychrophilum are major fish pathogens that cause diseases that may require antimicrobial therapy. Choice of appropriate treatment is dependent upon determining the antimicrobial susceptibility of isolates. Therefore we optimized methods for broth microdilution testing of F. columnare and F. psychrophilum to facilitate standardizing an antimicrobial susceptibility test. We developed adaptations to make reproducible broth inoculums and confirmed the proper incubation time and media composition. We tested the stability of potential quality-control bacteria and compared test results between different operators. Log phase occurred at 48 h for F. columnare and 72-96 h for F. psychrophilum, confirming the test should be incubated at 28°C for approximately 48 h and at 18°C for approximately 96 h, respectively. The most consistent susceptibility results were achieved with plain, 4-g/L, dilute Mueller-Hinton broth supplemented with dilute calcium and magnesium. Supplementing the broth with horse serum did not improve growth. The quality-control strains, Escherichia coli ATCC 25922 and Aeromonas salmonicida subsp. salmonicida ATCC 33658, yielded stable minimal inhibitory concentrations (MIC) against all seven antimicrobials tested after 30 passes at 28°C and 15 passes at 18°C. In comparison tests, most MICs of the isolates agreed 100% within one drug dilution for ampicillin, florfenicol, and oxytetracycline. The agreement was lower with the ormetoprim-sulfdimethoxine combination, but there was at least 75% agreement for all but one isolate. These experiments have provided methods to help standardize antimicrobial susceptibility testing of these nutritionally fastidious aquatic bacteria. Received June 24, 2015; accepted October 2, 2015.
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Affiliation(s)
- Charles M Gieseker
- a U.S. Food and Drug Administration , Center for Veterinary Medicine, Office of Research , 8401 Muirkirk Road, Laurel , Maryland 20708 , USA
| | - Tina C Crosby
- a U.S. Food and Drug Administration , Center for Veterinary Medicine, Office of Research , 8401 Muirkirk Road, Laurel , Maryland 20708 , USA
| | - Tamara D Mayer
- a U.S. Food and Drug Administration , Center for Veterinary Medicine, Office of Research , 8401 Muirkirk Road, Laurel , Maryland 20708 , USA
- b Present address: Sirenas Marine Discovery , 3550 General Atomics Court, San Diego , California 92121 , USA
| | - Sonya M Bodeis
- a U.S. Food and Drug Administration , Center for Veterinary Medicine, Office of Research , 8401 Muirkirk Road, Laurel , Maryland 20708 , USA
| | - Cynthia B Stine
- a U.S. Food and Drug Administration , Center for Veterinary Medicine, Office of Research , 8401 Muirkirk Road, Laurel , Maryland 20708 , USA
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Antibacterial activity of aquatic gliding bacteria. SPRINGERPLUS 2016; 5:116. [PMID: 26885469 PMCID: PMC4742450 DOI: 10.1186/s40064-016-1747-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Accepted: 01/28/2016] [Indexed: 11/10/2022]
Abstract
The study aimed to screen and isolate strains of freshwater aquatic gliding bacteria, and to investigate their antibacterial activity against seven common pathogenic bacteria. Submerged specimens were collected and isolated for aquatic gliding bacteria using four different isolation media (DW, MA, SAP2, and Vy/2). Gliding bacteria identification was performed by 16S rRNA gene sequencing and phylogenetic analysis. Crude extracts were obtained by methanol extraction. Antibacterial activity against seven pathogenic bacteria was examined by agar-well diffusion assay. Five strains of aquatic gliding bacteria including RPD001, RPD008, RPD018, RPD027 and RPD049 were isolated. Each submerged biofilm and plastic specimen provided two isolates of gliding bacteria, whereas plant debris gave only one isolate. Two strains of gliding bacteria were obtained from each DW and Vy/2 isolation medium, while one strain was obtained from the SAP2 medium. Gliding bacteria strains RPD001, RPD008 and RPD018 were identified as Flavobacterium anhuiense with 96, 82 and 96 % similarity, respectively. Strains RPD049 and RPD027 were identified as F. johnsoniae and Lysobacter brunescens, respectively, with similarity equal to 96 %. Only crude extract obtained from RPD001 inhibited growth of Listeria monocytogenes (MIC 150 µg/ml), Staphylococcus aureus (MIC 75 µg/ml) and Vibrio cholerae (MIC 300 µg/ml), but showed weak inhibitory effect on Salmonella typhimurium (MIC > 300 µg/ml). Gliding bacterium strain RPD008 should be considered to a novel genus separate from Flavobacterium due to its low similarity value. Crude extract produced by RPD001 showed potential for development as a broad antibiotic agent.
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Smith P, Endris R, Kronvall G, Thomas V, Verner-Jeffreys D, Wilhelm C, Dalsgaard I. Epidemiological cut-off values for Flavobacterium psychrophilum MIC data generated by a standard test protocol. JOURNAL OF FISH DISEASES 2016; 39:143-154. [PMID: 25546427 DOI: 10.1111/jfd.12336] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2014] [Accepted: 11/07/2014] [Indexed: 06/04/2023]
Abstract
Epidemiological cut-off values were developed for application to antibiotic susceptibility data for Flavobacterium psychrophilum generated by standard CLSI test protocols. The MIC values for ten antibiotic agents against Flavobacterium psychrophilum were determined in two laboratories. For five antibiotics, the data sets were of sufficient quality and quantity to allow the setting of valid epidemiological cut-off values. For these agents, the cut-off values, calculated by the application of the statistically based normalized resistance interpretation method, were ≤16 mg L(-1) for erythromycin, ≤2 mg L(-1) for florfenicol, ≤0.025 mg L(-1) for oxolinic acid (OXO), ≤0.125 mg L(-1) for oxytetracycline and ≤20 (1/19) mg L(-1) for trimethoprim/sulphamethoxazole. For ampicillin and amoxicillin, the majority of putative wild-type observations were 'off scale', and therefore, statistically valid cut-off values could not be calculated. For ormetoprim/sulphadimethoxine, the data were excessively diverse and a valid cut-off could not be determined. For flumequine, the putative wild-type data were extremely skewed, and for enrofloxacin, there was inadequate separation in the MIC values for putative wild-type and non-wild-type strains. It is argued that the adoption of OXO as a class representative for the quinolone group would be a valid method of determining susceptibilities to these agents.
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Affiliation(s)
- P Smith
- Department of Microbiology, School of Natural Sciences, National University of Ireland, Galway, Ireland
| | - R Endris
- Merck Animal Health, Summit, NJ, USA
| | - G Kronvall
- Department of Microbiology, Tumor and Cell Biology, Karolinska Institute, Stockholm, Sweden
| | - V Thomas
- MSD Animal Health Innovation, GmbH Zur Propstei, Schwabenheim, Germany
| | | | - C Wilhelm
- MSD Animal Health Innovation, GmbH Zur Propstei, Schwabenheim, Germany
| | - I Dalsgaard
- National Veterinary Institute, Technical University of Denmark, Frederiksburg, Denmark
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Entericidin is required for a probiotic treatment (Enterobacter sp. strain C6-6) to protect trout from cold-water disease challenge. Appl Environ Microbiol 2014; 81:658-65. [PMID: 25381243 DOI: 10.1128/aem.02965-14] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Flavobacterium psychrophilum causes bacterial cold-water disease in multiple fish species, including salmonids. An autochthonous Enterobacter strain (C6-6) inhibits the in vitro growth of F. psychrophilum, and when ingested as a putative probiotic, it provides protection against injection challenge with F. psychrophilum in rainbow trout. In this study, low-molecular-mass (≤3 kDa) fractions from both Enterobacter C6-6 and Escherichia coli K-12 culture supernatants inhibited the growth of F. psychrophilum. The ≤3-kDa fraction from Enterobacter C6-6 was analyzed by SDS-PAGE, and subsequent tandem mass spectroscopy identified EcnB, which is a small membrane lipoprotein that is a putative pore-forming toxin. Agar plate diffusion assays demonstrated that ecnAB knockout strains of both Enterobacter C6-6 and E. coli K-12 no longer inhibited F. psychrophilum (P < 0.001), while ecnAB-complemented knockout strains recovered the inhibitory phenotype (P < 0.001). In fish experiments, the engineered strains (C6-6 ΔecnAB and C6-6 ΔecnAB<pET101::ecnAB>) and the wild-type strain (C6-6) were added to the fish diet every day for 38 days. On day 11, the fish were challenged by injection with a virulent strain of F. psychrophilum (CSF 259-93). Fish that were fed C6-6 had significantly longer survival than fish fed the ecnAB knockout strain (P < 0.0001), while fish fed the complemented knockout strain recovered the probiotic phenotype (P = 0.61). This entericidin is responsible for the probiotic activity of Enterobacter C6-6, and it may present new opportunities for therapeutic and prophylactic treatments against similarly susceptible pathogens.
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Long A, Call DR, Cain KD. Investigation of the link between broodstock infection, vertical transmission, and prevalence of Flavobacterium psychrophilum in eggs and progeny of Rainbow Trout and Coho Salmon. JOURNAL OF AQUATIC ANIMAL HEALTH 2014; 26:66-77. [PMID: 24895859 DOI: 10.1080/08997659.2014.886632] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The etiological agent of bacterial coldwater disease (BCWD), Flavobacterium psychrophilum, can be transmitted both vertically and horizontally. Outbreaks of BCWD can result in significant losses in salmonid aquaculture. Reduction of outbreaks in fry may be possible through implementation of a management strategy in which progeny of heavily infected broodstock are culled from the general population. Diagnostic assays to quantify F. psychrophilum concentrations in tissue samples and confirm presence of the bacterium in ovarian fluid have been previously validated. In the current study, these assays were used to screen 60 female Rainbow Trout Oncorhynchus mykiss and 60 female Coho Salmon O. kisutch broodstock at two aquaculture facilities. Eyed eggs from 10 female broodstock (five fish from each facility) exhibiting graded levels of infection were transferred to the University of Idaho and monitored through early life stages for the presence of F. psychrophilum. Female Rainbow Trout broodstock were not positive for F. psychrophilum by enzyme-linked immunosorbent assay (ELISA) and prevalence was low in these progeny. However, ELISA optical density values for kidney correlated to F. psychrophilum prevalence in progeny (r = 0.938, P < 0.05) of Coho Salmon. Nested PCR on ovarian fluid was not a reliable indicator of vertical transmission in either species as broodstock ovarian fluid results did not correlate to F. psychrophilum prevalence in eyed eggs. Further research with these assays is necessary; however, results from this study indicate that broodstock screening may be a potential tool for evaluating F. psychrophilum infection levels, which could become an important component for disease management.
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Affiliation(s)
- Amy Long
- a Department of Fish and Wildlife Sciences and the Aquaculture Research Institute , University of Idaho , Post Office Box 441136, Moscow , Idaho 83844-1136 , USA
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Loch TP, Fujimoto M, Woodiga SA, Walker ED, Marsh TL, Faisal M. Diversity of fish-associated flavobacteria of Michigan. JOURNAL OF AQUATIC ANIMAL HEALTH 2013; 25:149-164. [PMID: 23834635 DOI: 10.1080/08997659.2012.758189] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Flavobacteriosis poses a serious threat to wild and propagated fish stocks alike, accounting for more fish mortality in Michigan and its associated state fish hatcheries than all other pathogens combined. Although this consortium of fish diseases has primarily been attributed to Flavobacterium psychrophilum, F. columnare, and F. branchiophilum, herein we describe a diverse assemblage of Flavobacterium and Chryseobacterium spp. isolates recovered from diseased as well as apparently healthy wild, feral, and farmed fish of Michigan. Among 254 fish-associated flavobacterial isolates recovered from 21 fish species during 2003-2010, 211 were identified as Flavobacterium spp., whereas 43 were identified as Chryseobacterium spp. according to ribosomal RNA partial gene sequencing and phylogenetic analysis. Although F. psychrophilum and F. columnare were indeed associated with multiple fish mortality events, many previously uncharacterized flavobacteria were recovered from systemically infected fish showing overt signs of disease, and in vitro protease assays demonstrated that these isolates were highly proteolytic to multiple substrates that comprise host tissues. Indeed, the majority of the isolates either (1) were most similar to recently described fish-associated Flavobacterium and Chryseobacterium spp. that have never before been reported in North America (e.g., F. oncorhynchi, F. araucananum, C. viscerum, C. piscicola, and C. chaponense) or (2) did not cluster with any described species and most likely represent novel flavobacterial taxa. This study highlights the extreme diversity of flavobacteria that are potentially associated with flavobacteriosis in Michigan.
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Affiliation(s)
- T P Loch
- a Department of Pathobiology and Diagnostic Investigation , College of Veterinary Medicine, Michigan State University , 174 Food Safety and Toxicology Building , East Lansing , Michigan , 48824 , USA
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Sundell K, Heinikainen S, Wiklund T. Structure of Flavobacterium psychrophilum populations infecting farmed rainbow trout Oncorhynchus mykiss . DISEASES OF AQUATIC ORGANISMS 2013; 103:111-119. [PMID: 23548361 DOI: 10.3354/dao02573] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Flavobacterium psychrophilum isolated from rainbow trout Oncorhynchus mykiss suffering from bacterial cold-water disease (BCWD) can dissociate into 2 morphological colony types, rough (R) and smooth (S). However, the presence of the 2 morphotypes in disease outbreaks has not yet been investigated thoroughly. We examined the occurrence of R and S morphotypes in rainbow trout from BCWD outbreaks and in unfertilized eggs from a hatchery. The isolated colony types were characterized by pulsed field gel electrophoresis (PFGE), plasmid analysis, and oxolinic acid susceptibility testing. From most outbreaks, both morphotypes were isolated, although the S type only was isolated from the majority of individual fish. PFGE analysis showed both diverse and indistinguishable genetic patterns among the concurrent morphotypes. While PFGE patterns common to both fish and egg isolates were identified, this was not always the case. Resistant and sensitive isolates of both colony types were isolated from individual disease outbreaks. The plasmid pattern was partly associated with the colony type, showing identical or completely different patterns for the R and S types isolated from the same outbreak. The study showed that within a BCWD outbreak, F. psychrophilum cells with different morphology, plasmid content, antibiotic susceptibility, and PFGE pattern can be isolated, suggesting that F. psychrophilum populations infecting rainbow trout in farm environments can be diverse and thus complicate the control of the disease.
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Burbank DR, Lapatra SE, Fornshell G, Cain KD. Isolation of bacterial probiotic candidates from the gastrointestinal tract of rainbow trout, Oncorhynchus mykiss (Walbaum), and screening for inhibitory activity against Flavobacterium psychrophilum. JOURNAL OF FISH DISEASES 2012; 35:809-816. [PMID: 22913277 DOI: 10.1111/j.1365-2761.2012.01432.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2011] [Revised: 10/31/2011] [Accepted: 11/22/2011] [Indexed: 06/01/2023]
Abstract
In this study, 318 bacterial strains were isolated from the gastrointestinal (GI) tracts of 29 rainbow trout, Oncorhynchus mykiss (Walbaum). These bacteria were screened in vitro for their ability to inhibit growth of Flavobacterium psychrophilum, the causative agent of coldwater disease. Bacteria observed to inhibit F. psychrophilum growth were further screened against rainbow trout bile, as an indicator of their ability to survive in the GI tract. This screening resulted in narrowing the pool to 24 bacterial isolates. Those 24 isolates were then tested for pathogenicity in rainbow trout by intraperitoneal injection. Following a 28-day challenge, eight isolates were shown to cause direct mortality and were eliminated from further study. As a result, 16 bacterial isolates were identified as probiotic candidates with the potential to control or reduce disease caused by F. psychrophilum.
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Affiliation(s)
- D R Burbank
- Department of Fish and Wildlife, University of Idaho, Moscow, ID, USA
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Long A, Polinski MP, Call DR, Cain KD. Validation of diagnostic assays to screen broodstock for Flavobacterium psychrophilum infections. JOURNAL OF FISH DISEASES 2012; 35:407-419. [PMID: 22486267 DOI: 10.1111/j.1365-2761.2012.01357.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
It is hypothesized that the frequency of bacterial coldwater disease outbreaks can be reduced through the detection of the aetiologic agent, Flavobacterium psychrophilum, in broodstock followed by culling of eggs from heavily infected broodstock. Before a culling programme can be instituted, however, it is necessary to determine the sensitivity and specificity of existing assays for the detection of F. psychrophilum. In this study, tissue and ovarian fluid samples were collected from 224 fish at five hatcheries and screened using an enzyme-linked immunosorbent assay (ELISA), a membrane-filtration fluorescent antibody test (MF-FAT), bacteriological culture and nested PCR. Latent class analysis was used to estimate sensitivity and specificity of kidney culture, kidney ELISA, nested PCR and MF-FAT. Analytical sensitivity of the ELISA varied but was greatest when bacteria were cultured under iron-limiting conditions. Diagnostic sensitivity estimates ranged from 0.02 (kidney culture) to 0.97 (kidney ELISA). Specificity estimates ranged from 0.02 (MF-FAT) to 0.98 (kidney ELISA). In a separate challenge experiment, the ELISA confirmed the presence of F. psychrophilum in sub-clinically infected fish. Results from this study demonstrate that the ELISA is an appropriate tool to screen broodstock and provides an indication of infection severity, which is crucial for implementation of a screening/culling programme.
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Affiliation(s)
- A Long
- Department of Fish and Wildlife Resources, University of Idaho, Moscow, ID, USA
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Zamora L, Fernández-Garayzábal J, Svensson-Stadler L, Palacios M, Domínguez L, Moore E, Vela A. Flavobacterium oncorhynchi sp. nov., a new species isolated from rainbow trout (Oncorhynchus mykiss). Syst Appl Microbiol 2012; 35:86-91. [DOI: 10.1016/j.syapm.2011.11.007] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Revised: 11/10/2011] [Accepted: 11/11/2011] [Indexed: 10/14/2022]
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Shah SQA, Nilsen H, Bottolfsen K, Colquhoun DJ, Sørum H. DNA gyrase and topoisomerase IV mutations in quinolone-resistant Flavobacterium psychrophilum isolated from diseased salmonids in Norway. Microb Drug Resist 2012; 18:207-14. [PMID: 22283604 DOI: 10.1089/mdr.2011.0142] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Flavobacterium psychrophilum is the causative agent of the recognized diseases 'bacterial coldwater disease' and 'rainbow trout fry syndrome' and is found in many farmed freshwater and marine fish species. In Norway, the bacterium has mainly been isolated from Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.). In the present study, 26 isolates from Norwegian farmed salmonids were examined. All isolates were tested for susceptibility towards various antibacterial drugs by the disk diffusion method, and minimum inhibitory concentration values for oxolinic acid and flumequine were established for selected isolates. All isolates from rainbow trout displayed reduced susceptibility towards quinolones, while brown trout and Atlantic salmon isolates were susceptible. The quinolone resistance determining regions (QRDRs) of the gyrA, gyrB, parC, and parE genes were sequenced. Sequence analysis of the QRDR of gyrA in quinolone resistant isolates revealed a threonine:arginine amino acid substitution at position 82 in all 16 isolates from Norwegian rainbow trout and a single reference strain isolated from rainbow trout in Sweden. No evidence for plasmid-mediated quinolone resistance was found in any of the isolates. Pulsed-field gel electrophoresis and phylogenetic analysis of parC and gyrB sequences indicate a clonal relationship between rainbow trout isolates.
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Affiliation(s)
- Syed Q A Shah
- Department of Food Safety & Infection Biology, Norwegian School of Veterinary Science, Oslo, Norway.
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