Papers by Bjarnheiður K Guðmundsdóttir
Rannsóknir eru undirstaða þróunar og hagsældar í landbúnaði
Rannsóknir og þróun eru undirstaða allra atvinnugreina. Atvinnugrein sem heldur ekki í við framfa... more Rannsóknir og þróun eru undirstaða allra atvinnugreina. Atvinnugrein sem heldur ekki í við framfarir og þróun þrífst ekki eða dafnar til lengdar. Á Tilraunastöð Háskóla Íslands í meinafraeði að Keldum eru stundaðar rannsóknir sem tengjast dýraheilbrigði og sjúkdómum í dýrum og mönnum. Þar er veitt ráðgjöf og þjónusta í þágu heilbrigðiseftirlits, sjúkdómagreininga og sjúkdóma varna fyrir búfé, eldisfiska og önnur dýr. Nemar í líffraeði, lífefnafraeði, lífeindafraeði og dýralaekningum vinna rannsóknarverkefni á fraeða sviðum stofnunarinnar sem hluta af grunn eða framhaldsnámi sínu. Með vaxandi innflutningi, hnatt vaeðingu og hlýnandi loftslagi má gera ráð fyrir að nýir smitsjúkdómar berist til landsins í auknum maeli. Fyrir utan haettulega smitsjúkdóma sem herja á búpening og geta valdið fjárhagslegu tjóni eru margir af varasömustu smit sjúkdómum í mönnum svokallaðar súnur (zoonosis), en það eru sýklar sem smitast úr dýrum í fólk (s.s. fuglaflensa, svínaflensa, ebólaveira og flei...
Journal of Fish Diseases, Nov 1, 2004
Moritella viscosa is the causative agent of winter ulcers in farmed salmonids and Atlantic cod in... more Moritella viscosa is the causative agent of winter ulcers in farmed salmonids and Atlantic cod in countries around the North Atlantic. The bacterium has also been isolated from various marine fish species. Bacterial diseases have been a limiting factor in farming of turbot, but M. viscosa has not so far been isolated. In this study, turbot was shown to be sensitive to M. viscosa infection in experimental challenges. Pathological changes in infected turbot were comparable with those previously described for winter ulcers in salmon. A multivalent commercial salmon vaccine, containing M. viscosa as one of five antigens and a mineral oil adjuvant, did not protect turbot against challenge 13 weeks postvaccination. Weight gain of vaccinated turbot compared with controls was not reduced 7 weeks post-vaccination. Vaccination did not induce a specific anti-M. viscosa response, while elevated anti-M. viscosa antibody levels were detected both in vaccinated and unvaccinated fish 5 weeks postchallenge. The vaccine did, however, induce an antibody response against Aeromonas salmonicida, another vaccine component. Minor intra-abdominal adhesions were detected in vaccinated fish and fish injected with a mineral oil adjuvant. The measurement of various innate humoral immune parameters did not reveal significant differences between vaccinated and control groups.
Journal of Fish Diseases, Oct 1, 2014
The metalloendopeptidase AsaP1 is one of the major extracellular virulence factors of A. salmonic... more The metalloendopeptidase AsaP1 is one of the major extracellular virulence factors of A. salmonicida subsp. achromogenes, expressed as a 37-kDa pre-pro-peptide and processed to a 19-kDa active peptide. The aim of this study was to construct mutant strains secreting an AsaP1-toxoid instead of AsaP1-wt, to study virulence of these strains and to test the potency of the AsaP1-toxoid bacterin and the recombinant AsaP1-toxoids to induce protective immunity in Arctic char. Two A. salmonicida mutants were constructed that secrete either AsaP1 E294A or AsaP1 Y309F. The secreted AsaP1 Y309F-toxoid had weak caseinolytic activity and was processed to the 19-kDa peptide, whereas the AsaP1 E294A-toxoid was found as a 37-kDa pre-pro-peptide suggesting that AsaP1 is auto-catalytically processed. The LD 50 of the Asa-P1 Y309F-toxoid mutant in Arctic char was significantly higher than that of the corresponding wt strain, and LD 50 of the AsaP1 E294A-toxoid mutant was comparable with that of an AsaP1-deficient strain. Bacterin based on AsaP1 Y309F-toxoid mutant provided significant protection, comparable with that induced by a commercial polyvalent furunculosis vaccine. Detoxification of AsaP1 is very hard, expensive and time consuming. Therefore, an AsaP1-toxoid-secreting mutant is more suitable than the respective wt strain for production of fish bacterins aimed to protect against atypical furunculosis.
FEBS Letters, Sep 1, 2016
The Gram-negative bacterium Aeromonas salmonicida is a fish pathogen for various fish species wor... more The Gram-negative bacterium Aeromonas salmonicida is a fish pathogen for various fish species worldwide. Aeromonas salmonicida subsp. achromogenes produces the extracellular, toxic zinc endopeptidase AsaP1. Crystal structure analyses at 2.0 A resolution of two proteolytically inactive AsaP1 variants show the polypeptide folding of the protease domain and the propeptide domain. These first crystal structure analyses of a precursor of a deuterolysin-like aspzincin protease provide insights into propeptide function, and specific substrate binding. A lysine side chain of the propeptide binds in the hydrophobic S1'-pocket interacting with three carboxylate side chains. An AsaP1 variant with a lysine to alanine exchange identifies the chaperone function of the propeptide.
Survival and humoral antibody response of Atlantic salmon, <i>Salmo salar</i> L., vaccinated against <i>Aeromonas salmonicida</i> ssp. <i>achromogenes</i>
Journal of Fish Diseases, Sep 1, 1997
Atlantic salmon were vaccinated against Aeromonas salmonicida ssp. achromogenes (Asa) by injectio... more Atlantic salmon were vaccinated against Aeromonas salmonicida ssp. achromogenes (Asa) by injection with three vaccines developed in our laboratory and an autogenous bacterin (IcelandBiojec.OO, IBOO) produced by a commercial vaccine producer. The humoral antibody responses to bacterial antigens were monitored by ELISA and Western blotting. The fish were challenged by infection with Asa 6 and 12 weeks post‐vaccination. Protection was induced in all groups of vaccinated fish. The protection achieved was time‐dependent. The autogenous bacterin, IBOO, induced a protective immune response later than our experimental vaccines. All the vaccines tested induced specific antibody response that increased between 6 and 12 weeks after vaccination. The antibody response was mainly directed against the A‐layer protein, but antibodies to other bacterial components were also detected. Significant correlation was obtained between the antibody titre to extracellular Asa antigens, induced by the different vaccine preparations, and survival of vaccinated fish challenged by a virulent Asa strain. Furthermore, the detection of antibodies directed against an extracellular toxic metallo‐caseinase, AsaP1, in fish sera correlated with protection.
Vaccine, Jul 1, 2007
Atypical furunculosis is a problem in farming of salmonids and various other fish species caused ... more Atypical furunculosis is a problem in farming of salmonids and various other fish species caused by a heterogeneous group of atypical Aeromonas salmonicida strains. Winter ulcer is a disease of salmonids and cod caused by Moritella viscosa, but a number of fish species are susceptible to the infection. Vaccines are available against atypical furunculosis of salmonids, but their efficacy is dependent on the characteristics of the infective strain. Vaccines for non-salmonid fish are currently not commercially available. Furunculosis vaccines for salmon can induce cross protection against some atypical A. salmonicida infections and only in some fish species. Polyvalent injection vaccines based on inactivated bacterial cells are available against winter ulcer disease of salmonids. Outbreaks of winter ulcer disease in vaccinated salmon are, however, continuously reported.
<i>Aeromonas salmonicida</i> and <i>A. hydrophila</i>
CABI eBooks, 2017
Antibody response in salmonids against the 70 kDa serine protease of Aeromonas salmonicida studied by a monoclonal antibody-based ELISA
Veterinary Immunology and Immunopathology, Sep 1, 2001
An antigen-capture enzyme-linked immunosorbent assay (cELISA) based on monoclonal antibodies (mAb... more An antigen-capture enzyme-linked immunosorbent assay (cELISA) based on monoclonal antibodies (mAb) was set up and evaluated for selective detection of salmonid antibody responses to the antigen P1, which is a weakly immunogenic exoprotease of typical Aeromonas salmonicida. This new assay permits a specific determination of anti-protease-antibodies, without antigen purification. Serum antibodies induced by the strongly immunogenic lipopolysaccharide could reliably be discriminated from anti-P1-antibodies. Antibody titres of 45 experimental antisera recorded by cELISA were moderately correlated with titres determined by routinely used indirect ELISA (iELISA) by detecting partially different antibody populations (r=0.753). Substitutions of immunoreactants and confirmatory immunoblotting strongly suggest that the mAb-based assay selectively recognises antibodies directed to epitopes of native protease. A conjugate of inhibited protease and cationized bovine serum albumin (cBSA) was found to engender a significant anti-protease-response in three salmonid species (P&lt;0.05), whereas the unconjugated antigen and Apoject 1-Fural were proved to be ineffective. Recorded specific antibody titres were as high as 1:381,400, indicating a considerable enhanced immunogenicity of cBSA-conjugated P1 and high assay sensitivity. The established cELISA offers a promising approach to further improvement of monitoring fish humoral immune response to surface accessible epitopes of the immunosuppressive exoprotease, P1, and to scrutinize its protective significance.
Monoclonal antibodies against AsaP1, a major exotoxin of the fish pathogen Aeromonas salmonicida subsp. achromogenes, and their application in ELISA
Journal of Applied Microbiology, Oct 1, 1999
Two monoclonal antibodies (Mabs) binding to a toxic extracellular metallo-proteinase of Aeromonas... more Two monoclonal antibodies (Mabs) binding to a toxic extracellular metallo-proteinase of Aeromonas salmonicida subsp. achromogenes, AsaP1, were produced. Both reacted with common epitopes of the native enzyme and recognized this 20 kDa antigen on Western blots. One of these Mabs had an inhibitory effect on the caseinase activity of the exotoxin. A Mab-based ELISA was set up and evaluated for serological detection of AsaP1 in bacterial culture filtrates. The exotoxin was identified serologically in the extracellular products of 11 of 26 atypical Aer. salmonicida isolates, including the type strain for subsp. achromogenes NCIMB 1110. The ELISA was approximately 100-fold more sensitive in detecting AsaP1 compared with an azocasein assay. The established serological test enables AsaP1 to be quantified reliably with a lower detection limit of about 0.12 ng ml-1 and has a potential use for the phenotypic differentiation of atypical Aer. salmonicida isolates.
Systematic and Applied Microbiology, Mar 1, 1998
Fifty two isolates of atypical Aeromonas salmonicida, recovered from a wide range of hosts and ge... more Fifty two isolates of atypical Aeromonas salmonicida, recovered from a wide range of hosts and geographical locations, were heterogeneous in terms of molecular and phenotypic characteristics, and represented taxa which could not be accommodated by the current classification of four subspecies. Generally, there was incongruence between the molecular (PCR, RAPD and ribotyping) and phenotypic methods in terms of cluster membership. By PCR, 6 groups were described of which Group 1 encompassed 12 isolates including the type strain of A. salmonicida subsp. smithia. Group 2 accommodated 23 isolates including the reference cultures of subspecies achromogenes and masoucida. The named culture of Haemophilus piscium was recovered in Group 6. By ribotyping and RAPD, the reference cultures were recovered in separate groups. All methods pointed to the uniqueness of subspecies smithia. Most isolates contained 2-6 plasmids, of 2.3 to 150 kb in length. Nevertheless, all isolates possessed certain key characteristics, including Gram-negativity, and the absence of motility.
FEBS letters, Sep 1, 2016
The Gram-negative bacterium Aeromonas salmonicida is a fish pathogen for various fish species wor... more The Gram-negative bacterium Aeromonas salmonicida is a fish pathogen for various fish species worldwide. Aeromonas salmonicida subsp. achromogenes produces the extracellular, toxic zinc endopeptidase AsaP1. Crystal structure analyses at 2.0 Å resolution of two proteolytically inactive AsaP1 variants show the polypeptide folding of the protease domain and the propeptide domain. These first crystal structure analyses of a precursor of a deuterolysin-like aspzincin protease provide insights into propeptide function, and specific substrate binding. A lysine side chain of the propeptide binds in the hydrophobic S1'-pocket interacting with three carboxylate side chains. An AsaP1 variant with a lysine to alanine exchange identifies the chaperone function of the propeptide.
Acta crystallographica, Jul 1, 2009
Two mutants of the toxic extracellular zinc endopeptidase AsaP1 (AsaP1_ E294Q and AsaP1_E294A) of... more Two mutants of the toxic extracellular zinc endopeptidase AsaP1 (AsaP1_ E294Q and AsaP1_E294A) of Aeromonas salmonicida subsp. achromogenes were expressed in Escherichia coli and crystallized by the vapour-diffusion method. Crystals were obtained using several precipitants and different protein concentrations. Protein crystals were found in a monoclinic (C2) as well as an orthorhombic (P2 1 2 1 2 1) space group. The crystals belonging to the monoclinic space group C2 had unit-cell parameters a = 103.4, b = 70.9, c = 54.9 Å , = 109.3 for AsaP1_E294A, and a = 98.5, b = 74.5, c = 54.7 Å , = 112.4 for AsaP1_ E294Q. The unit-cell parameters of the orthorhombic crystal obtained for AsaP1_E294A were a = 57.9, b = 60.2, c = 183.6 Å. The crystals of the two different mutants diffracted X-rays beyond 2.0 Å resolution.
Acta Crystallographica Section F-structural Biology and Crystallization Communications, 2009
Two mutants of the toxic extracellular zinc endopeptidase AsaP1 (AsaP1_ E294Q and AsaP1_E294A) of... more Two mutants of the toxic extracellular zinc endopeptidase AsaP1 (AsaP1_ E294Q and AsaP1_E294A) of Aeromonas salmonicida subsp. achromogenes were expressed in Escherichia coli and crystallized by the vapour-diffusion method. Crystals were obtained using several precipitants and different protein concentrations. Protein crystals were found in a monoclinic (C2) as well as an orthorhombic (P2 1 2 1 2 1) space group. The crystals belonging to the monoclinic space group C2 had unit-cell parameters a = 103.4, b = 70.9, c = 54.9 Å , = 109.3 for AsaP1_E294A, and a = 98.5, b = 74.5, c = 54.7 Å , = 112.4 for AsaP1_ E294Q. The unit-cell parameters of the orthorhombic crystal obtained for AsaP1_E294A were a = 57.9, b = 60.2, c = 183.6 Å. The crystals of the two different mutants diffracted X-rays beyond 2.0 Å resolution.
Sjúkdómar í eldisþorski
ÁGRIP Í þessu riti er gerð grein fyrir sjúkdómum sem gaetir á mismunandi þroskastigum þorsksins, ... more ÁGRIP Í þessu riti er gerð grein fyrir sjúkdómum sem gaetir á mismunandi þroskastigum þorsksins, allt frá frumfóðrun þorsklirfa til seiðaeldis í strandkerum og síðan áframeldis á sláturfiski í sjókvíum. Einnig er fjallað um helstu eiginleika ónaemiskerfis fiska, með áherslu á þorsk, og í hverju það er frábrugðið því sem gerist meðal dýra með heitt blóð. Áhersla er lögð á stöðu mála hér á landi. Í íslensku þorskeldi hefur gaett svipaðra sjúkdómsvalda og í þorskeldi erlendis. Bakteríusýkingar sem helst hafa látið til sín taka, enn sem komið er, eru kýlaveikibróðir (Aeromonas salmonicida undirtegund achromogenes) og vibríuveiki (Listonella anguillarum). Auk þess hefur orðið vart Flexibacter-sýkingar á roði þorsks. Utan á tálknum og roði gaetir helst sýkinga af völdum einfruma sníkjudýra (Ichthyobodo tegund og Trichodina tegundir). Sýkingar af völdum tveggja annarra tegunda frumdýra, annars vegar í tálknum og ýmsum innri líffaerum (Loma tegund) og hins vegar í gervitálknum (X-cell disea...
Comparing methods for environmental shading during
High mortality rates commonly observed during the early life stages of intensively reared Atlanti... more High mortality rates commonly observed during the early life stages of intensively reared Atlantic halibut have among other things been related to high bacterial numbers and an unfavourable bacterial community The study describes the effects of two different methods for environmental shading on larval survival and numbers of cultivable bacteria in the culture water and the gastrointestinal
Veterinary Microbiology, 2013
Aeromonas salmonicida subsp. achromogenes is the causative agent of atypical furunculosis in many... more Aeromonas salmonicida subsp. achromogenes is the causative agent of atypical furunculosis in many fish species, including Atlantic salmon (Salmon salar L.) and Arctic charr (Salvelinus alpinus L.) (Gudmundsdottir and Bjornsdottir, 2007). Detoxified, concentrated extracellular products (ECP) of A. salmonicida subsp. achromogenes induce a better
Vaccine, 2007
Atypical furunculosis is a problem in farming of salmonids and various other fish species caused ... more Atypical furunculosis is a problem in farming of salmonids and various other fish species caused by a heterogeneous group of atypical Aeromonas salmonicida strains. Winter ulcer is a disease of salmonids and cod caused by Moritella viscosa, but a number of fish species are susceptible to the infection. Vaccines are available against atypical furunculosis of salmonids, but their efficacy is dependent on the characteristics of the infective strain. Vaccines for non-salmonid fish are currently not commercially available. Furunculosis vaccines for salmon can induce cross protection against some atypical A. salmonicida infections and only in some fish species. Polyvalent injection vaccines based on inactivated bacterial cells are available against winter ulcer disease of salmonids. Outbreaks of winter ulcer disease in vaccinated salmon are, however, continuously reported.
Journal of Fish Diseases, 2003
Atlantic halibut, Hippoglossus hippoglossus (L.), was shown to be sensitive to infection by three... more Atlantic halibut, Hippoglossus hippoglossus (L.), was shown to be sensitive to infection by three different isolates of Aeromonas salmonicida ssp. achromogenes in pre‐challenge tests using intraperitoneal (i.p.) and intramuscular (i.m.) injections as well as bath challenges. A commercial furunculosis vaccine, Alphaject 1200, and an autogenous vaccine, AAS, based on the challenge strain, induced immune protection as shown in challenge tests 8 weeks post‐immunization. The survival rate of vaccinated fish after i.p. challenge was 100%, whereas mortality of control fish was 61%. Employing i.m. challenge, relative percentage survival induced by the furunculosis vaccine and the AAS vaccine was 47 and 44, respectively. Mortality of i.m. injected controls was 68%. Vaccinated fish behaved normally following vaccination but the weight gain was significantly reduced in vaccinated fish 8 weeks post‐vaccination compared with control fish receiving phosphate‐buffered saline. At the same time, int...
Survival and humoral antibody response of Atlantic salmon, Salmo salar L., vaccinated against Aeromonas salmonicida ssp. achromogenes
Journal of Fish Diseases, 1997
Atlantic salmon were vaccinated against Aeromonas salmonicida ssp. achromogenes (Asa) by injectio... more Atlantic salmon were vaccinated against Aeromonas salmonicida ssp. achromogenes (Asa) by injection with three vaccines developed in our laboratory and an autogenous bacterin (IcelandBiojec.OO, IBOO) produced by a commercial vaccine producer. The humoral antibody responses to bacterial antigens were monitored by ELISA and Western blotting. The fish were challenged by infection with Asa 6 and 12 weeks post‐vaccination. Protection was induced in all groups of vaccinated fish. The protection achieved was time‐dependent. The autogenous bacterin, IBOO, induced a protective immune response later than our experimental vaccines. All the vaccines tested induced specific antibody response that increased between 6 and 12 weeks after vaccination. The antibody response was mainly directed against the A‐layer protein, but antibodies to other bacterial components were also detected. Significant correlation was obtained between the antibody titre to extracellular Asa antigens, induced by the differe...
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Papers by Bjarnheiður K Guðmundsdóttir