This study focused on the enzyme, aspartate transcarbamoylase (ATCase) from A. hydrophila, a Gram-negative bacterium found in fresh water. The molecular mass of the ATCase holoenzyme from A. hydrophila is 310 kDa. The enzyme is likely composed of 6 catalytic polypeptides of 34 kDa each and 6 regulatory polypeptides of 17 kDa each. The velocity-substrate curve for A. hydrophila ATCase is sigmoidal for both aspartate and carbamoylphosphate. The Km for aspartate was the highest to date for an enteric bacterium at 97.18 mM. The Km for carbamoylphosphate was 1.18 mM. When heated to 60 ºC, the specific activity of the enzyme dropped by more than 50 %. When heated to 100 ºC, the enzyme showed no activity. The enzyme's activity was inhibited by ATP, CTP or UTP.

Yes / Aeromonas hydrophila is a well-known waterborne pathogen that recently was found to infect humans. Here, we report the draft genome of a freshwater isolate from a Malaysian waterfall, A. hydrophila strain M023, which portrays N-acylhomoserine lactone-dependent quorum sensing. / University of Malaya via High Impact Research Grants (UM C/625/1/HIR/MOHE/CHAN/01, A-000001-50001, and UM C/625/1/HIR/MOHE/CHAN/14/1, H-50001-A000027)

Disease outbreaks have overwhelmed the aquaculture industry as a whole and have been catastrophic for many single operations. To minimize disease outbreaks, efforts are underway to enhance animal health and disease resistance to pathogens without the use of antibiotics. The overall purpose of this study was to explore a potential prophylactic, a novel antibody diet, for the bacterial pathogen, Aeromonas hydrophila, in tilapia. The tilapia were on an anti-interleukin-10 antibody diet as a neutralization of interleukin-10 (IL-10), an anti-inflammatory cytokine. The anti-inflammatory function of IL-10 has been shown to allow persistence of gastrointestinal pathogens. Tilapia were fed the novel diet and were challenged via bath immersion or oral gavage with A. hydrophila. Four trials of challenge studies were conducted. Clinical signs of the disease and survival were monitored post-challenge of the bacteria. Out of the 4 trials, one bath immersion trial showed significantly lower survival in the group fed the novel antibody diet (p=0.044) compared to the control fed group, after challenged with A. hydrophila. The other trials tested showed no significant differences in survival between diets. Among the survival percentages collected as a whole, it cannot be determined from in vivo results whether this anti-IL-10 diet is effective in preventing mortality from A. hydrophila in tilapia. Therefore, an in vitro study using an enzyme-linked immunosorbent assay (ELISA) was used to determine the neutralization capability of anti-IL-10 on IL-10 using tilapia splenocytes. Interferon-γ, a pro-inflammatory cytokine, was quantified in order to find a trend in expression of IL-10 in vitro in various tilapia cell treatments. The protocol for the ELISA study is under development being that the use of this antibody is novel and has never before been done in fish. / Master of Science in Life Sciences

VASCONCELOS, Fábio Roger. Bactérias com Potencial Biotecnológico na Descoloração de Corantes Têxteis. 2010. 64 f. : Dissertação (mestrado) - Universidade Federal do Ceará, Centro de Ciências Agrárias, Departamento de Engenharia de Pesca, Fortaleza-CE, 2010 / Submitted by Nádja Goes (nmoraissoares@gmail.com) on 2016-07-14T12:39:39Z No. of bitstreams: 1 2010_dis_frvasconcelos.pdf: 490074 bytes, checksum: c033f812460c47d5fd980f329dc81fa3 (MD5) / Approved for entry into archive by Nádja Goes (nmoraissoares@gmail.com) on 2016-07-14T12:40:02Z (GMT) No. of bitstreams: 1 2010_dis_frvasconcelos.pdf: 490074 bytes, checksum: c033f812460c47d5fd980f329dc81fa3 (MD5) / Made available in DSpace on 2016-07-14T12:40:02Z (GMT). No. of bitstreams: 1 2010_dis_frvasconcelos.pdf: 490074 bytes, checksum: c033f812460c47d5fd980f329dc81fa3 (MD5) Previous issue date: 2010 / The discharge of effluents from textile industries for water bodies is currently a major concern for environmentalists as a function of synthetic dyes used to color fabrics thus polluting the environment. Biological treatments, especially with the use of bacteria, present themselves as the most economically viable and widely used to decolorize colored effluents. Thus, studies were conducted to test the color removal of dyes Remazol Brilliant Blue R, Orange G and Orange II using isolated and in mixed culture strains of Escherichia coli and Aeromonas hydrophila. Firstly, the isolation of bacterial strains from three different environments was made. Then, tests were performed to verify that the dye concentration would limit the growth of each microorganism. In addition to tests of decolorization, other parameters such as pH, biomass, COD removal, total protein and toxicity of metabolites were also monitored. The Escherichia coli strain isolated from the marine environment was able to decolorize concentrations of 2, 5 and 2 mg L-1, respectively, for the RBBR dye, Orange G and Orange II dyes, while the strain E. coli isolated from textile effluent, decolorized in concentrations of 5, 0.5 and 5 mg L-1, respectively. The bacteria Aeromonas hydrophila decolorized, respectively, at 10, 5 and 5 mg L-1, while the consortium of three bacteria decolorized at concentration of 5 mg L-1 for the three dyes tested individually. In these culture conditions the decrease in the rate of COD ranged from 45% to 69% with the lowest rate observed in the assay containing A. hydrophila and dye Orange II (45%) and the highest removal rate in the test containing the dye RBBR and the consortium (69%). Bioassays using Artemia salina showed that during the process of decolorization metabolites were produced with recalcitrant characteristics. The results show that the bacteria Escherichia coli and Aeromonas hydrophila have biotechnological potential in textile dyes, provided that they use low dye concentrations decolorizing / A descarga de efluentes das indústrias têxteis para corpos aquosos é, correntemente, uma das maiores preocupações dos ambientalistas em função dos corantes sintéticos usados para colorir os tecidos poluindo assim o ambiente. A aplicação de tratamentos biológicos, sobretudo com a utilização de bactérias, apresenta-se como um dos mais viáveis economicamente, sendo um dos sistemas mais utilizados para descolorir efluentes coloridos. Neste sentido, estudos foram realizados testes para a remoção de cor dos corantes Remazol Brilliant Blue R, Orange G e Orange II utilizando cepas de Escherichia coli e de Aeromonas hydrophila, isoladas e em cultura mista. Primeiramente foi feito o isolamento das cepas bacterianas de três ambientes diferentes. Em seguida, foram feitos testes para verificar qual concentração do corante seria limite para o crescimento de cada microrganismo. Além dos testes de descoloração também foram monitorados outros parâmetros como o pH, biomassa, remoção de DQO, proteínas totais e toxicidade dos metabólitos formados. A cepa Escherichia coli, isolada do ambiente marinho, foi capaz de descolorir concentrações de 2, 5 e 2 mg L-1, respectivamente, para os corante RBBR, Orange G e Orange II, enquanto que a cepa E. coli, isolada do efluente têxtil, descoloriu nas concentrações de 5, 0,5 e 5 mg L-1, respectivamente. A bactéria Aeromonas hydrophila descoloriu respectivamente nas concentrações de 10, 5 e 5 mg L-1, enquanto que o consórcio das três bactérias descoloriu na concentração de 5 mg L-1 para os três corantes testados individualmente. Nessas condições de cultivo a diminuição na taxa de DQO variou entre 45 e 69%, com a menor taxa observada no ensaio contendo A. hydrophila e o corante Orange II (45%) e a maior taxa de remoção no ensaio contendo o consórcio e o corante RBBR (69%). Bioensaios utilizando o microcrustáceo Artemia salina mostraram que durante o processo de descoloração foram produzidos metabólitos com características recalcitrantes. Os resultados demonstram que as bactérias Escherichia coli e Aeromonas hydrophila apresentam potencial biotecnológico na descoloração de corantes têxteis, desde que sejam utilizadas baixas concentrações dos corantes

Aeromonas hydrophila is distributed widely in nature and is responsible for an array of human infections. Several studies on the isolation and characterisation of the organism abound. Although there are reports on the antibiotic resistance profiles of the organism, these reports have not been updated in Limpopo province, South Africa despite the established fact that antibiograms vary with time and geographical area. Antibiotic resistance and pathogenesis of an organism are dependent on a host of factors such as the production of extended spectrum beta-lactamases and the genetic profiles such as the genes coding for resistance and possession of integrons and how these characteristics overach with the phylogenetic inter-relatedness of isolates from different sources. In spite of the aforementioned concerns on the efficacy of antibiotics due to the acquisition or endowment of microorganisms with intrinsic and extrinsic factors , which enhances resistance to antibiotics , medicinal plants are reportedly offering promise as alternative sources of efficacious management of infections. Medicinal plants are employed by traditional healers in the management of infections in developing countries especially in Africa. However, the antimicrobial activities of medicinal plants against Aeromonas hydrophila have received only a cursory attention. In an endeavour to undertake a comprehensive study on the isolation, characterisation, antibiograms, activities of medicinal plants as well as the genetic profiles, including phylogenetics relatedness of Aeromonas isolates from different sources, stool and water samples were collected over a two year period from designated places in Limpopo Province and analysed using standard techniques applicable to the constituent research activity. The research findings are presented in six chapters as presented hereunder. The first chapter focussed on the literature review of the organism and reflects areas such as the morphology, laboratory diagnosis, clinical manifestations, pathogenesis, antimicrobial susceptibility profiles, antibacterial activities of medicinal plants as well as the genetic aspects of Aeromonas hydrophila. / Environmental Science / D.Phil. (Environmental Science)

Introdução: Bactérias do gênero Aeromonas estão presentes em ambientes de água doce, salgada e salobra. O isolamento destes microrganismos já foi relatado em água de abastecimento público e alimentos. Algumas espécies podem ser patogênicas ao homem, causando gastrenterites e outras infecções. Isolados de Aeromonas de fontes diversas expressam resistência a antimicrobianos, especialmente a -lactâmicos, devido à presença de enzimas -lactamases. A patogenicidade das espécies se deve à virulência multifatorial, que compreende a produção de enterotoxinas (Act, Alt e Ast), de elastase, presença de flagelo, entre outros. Objetivo: Isolar, identificar e quantificar Aeromonas hydrophila isoladas de esgoto e lodo tratado; pesquisar a ocorrência dos genes de virulência e resistência a -lactâmicos. Material e Métodos: A detecção e quantificação de Aeromonas hydrophila foram realizadas por meio da técnica de membrana filtrante e meio de cultura específico; a identificação foi realizada por meio da PCR utilizando um par de primers específicos para a espécie. Após a confirmação da espécie foi realizado o antibiograma para conhecer o perfil de resistência aos antibióticos; a pesquisa dos genes de virulência act, alt, ast, ela, lip e fla e genes de resistência a -lactâmicos foi realizada por meio da PCR e seqüenciamento. Resultados: Foram analisadas 15 amostras (seis de esgoto tratado e nove de lodo tratado). Destas, somente nove foram positivas para A. hydrophila, obtendo-se 441 colônias típicas, das quais 348 foram positivas, por PCR para identificação do gênero e 209 para identificação da espécie. Os 209 isolados, sendo 92 do esgoto tratado e 117 do lodo tratado, apresentaram os seguintes valores na pesquisa dos genes de virulência: 36 por cento (act), 40 por cento (ast), 78 por cento (alt), 82 por cento (fla), 86 por cento (lip) e 87 por cento (ela) e 100 por cento dos isolados apresentaram pelo menos um dos genes. Para os testes de sensibilidade aos antibióticos todos os isolados foram resistentes a pelo menos um dos antibióticos. A produção de enzimas MBL, ESBL e AmpC foi detectada em isolados. Também foram encontrados genes de resistência cphA, bla TEM e bla MOX, enquanto que os genes bla VIM, bla IMP, bla e bla não foram detectados. Conclusão: Os resultados sugerem que A. hydrophila pode resistir ao processo de tratamento de esgoto e lodo, além disso, pode apresentar diversos genes de virulência e resistência a antibióticos, motivos pelos quais A. hydrophila pode ser uma ameaça a Saúde Pública, uma vez que estas amostras são reutilizadas para fins urbanos ou agrícolas / Introduction: Bacteria of the genus Aeromonas are present in fresh, brackish and salty waters. The isolation of these microorganisms has been reported in public water supplies and foods. Some species can be pathogenic to humans, causing gastroenteritis and other infections. Aeromonas isolates from different sources express resistance to antimicrobials, especially -lactams, due to the presence of lactamase enzymes. The pathogenicity of the species is due to the multifactorial virulence, wich includes the production of enterotoxins (Act, Alt and Ast) of Elastase and presense of flagello, among others. Objectives: Identify and quantify Aeromonas hydrophila isolated from treated wastewater and sludge, to investigate the occurrence of virulence genes and resistance to -lactams. Material and methods: The detection and quantification of A. hydrophila were made through the membrane filter technique and specific culture medium, the identification was performed by PCR using a pair of primers specific for the species. After confirming the species sensitivity was performed to know the profile of antibiotic resistance, the survey of virulence genes act, alt, ast, ela, lip, fla and resistance to -lactams gene was performed by PCR and sequencing. Results: We analyzed 15 samples (six of nine treated wastewater and sludge). Of these only nine were positive for A. hydrophila, resulting in 441 typical colonies, of wich 348 were positive by PCR to identify the genus and 209 for species identification. The 209 isolates, being 92 and 117 of treated wastewater and treated sludge showed the following values in the study of the virulence genes: 36 per cent (act), 78 per cent (alt), 82 per cent (fla), 86 per cent (lip), 87 per cent (ela) and 100 per cent of the isolates had at least one of the genes. For antibiotic susceptibility testing all isolates were resistant to at least one antibiotic. The production of MBL, ESBL and AmpC enzyme was detected in isolates. It was also found resistance genes cphA, bla TEM and bla MOX, while genes bla VIM , bla IMP , bla and bla FOX CTX-M were not detected. Conclusion: The results suggest that A. hydrophila can resist the process of treating of wastewater and sludge, moreover, may have different virulence genes and antibiotic resistance, which is why A. hydrophila can be a threat to public health, since these samples are reused for agricultural or urban purposes. , bla SHV

Introdução: Bactérias do gênero Aeromonas estão presentes em ambientes de água doce, salgada e salobra. O isolamento destes microrganismos já foi relatado em água de abastecimento público e alimentos. Algumas espécies podem ser patogênicas ao homem, causando gastrenterites e outras infecções. Isolados de Aeromonas de fontes diversas expressam resistência a antimicrobianos, especialmente a -lactâmicos, devido à presença de enzimas -lactamases. A patogenicidade das espécies se deve à virulência multifatorial, que compreende a produção de enterotoxinas (Act, Alt e Ast), de elastase, presença de flagelo, entre outros. Objetivo: Isolar, identificar e quantificar Aeromonas hydrophila isoladas de esgoto e lodo tratado; pesquisar a ocorrência dos genes de virulência e resistência a -lactâmicos. Material e Métodos: A detecção e quantificação de Aeromonas hydrophila foram realizadas por meio da técnica de membrana filtrante e meio de cultura específico; a identificação foi realizada por meio da PCR utilizando um par de primers específicos para a espécie. Após a confirmação da espécie foi realizado o antibiograma para conhecer o perfil de resistência aos antibióticos; a pesquisa dos genes de virulência act, alt, ast, ela, lip e fla e genes de resistência a -lactâmicos foi realizada por meio da PCR e seqüenciamento. Resultados: Foram analisadas 15 amostras (seis de esgoto tratado e nove de lodo tratado). Destas, somente nove foram positivas para A. hydrophila, obtendo-se 441 colônias típicas, das quais 348 foram positivas, por PCR para identificação do gênero e 209 para identificação da espécie. Os 209 isolados, sendo 92 do esgoto tratado e 117 do lodo tratado, apresentaram os seguintes valores na pesquisa dos genes de virulência: 36 por cento (act), 40 por cento (ast), 78 por cento (alt), 82 por cento (fla), 86 por cento (lip) e 87 por cento (ela) e 100 por cento dos isolados apresentaram pelo menos um dos genes. Para os testes de sensibilidade aos antibióticos todos os isolados foram resistentes a pelo menos um dos antibióticos. A produção de enzimas MBL, ESBL e AmpC foi detectada em isolados. Também foram encontrados genes de resistência cphA, bla TEM e bla MOX, enquanto que os genes bla VIM, bla IMP, bla e bla não foram detectados. Conclusão: Os resultados sugerem que A. hydrophila pode resistir ao processo de tratamento de esgoto e lodo, além disso, pode apresentar diversos genes de virulência e resistência a antibióticos, motivos pelos quais A. hydrophila pode ser uma ameaça a Saúde Pública, uma vez que estas amostras são reutilizadas para fins urbanos ou agrícolas / Introduction: Bacteria of the genus Aeromonas are present in fresh, brackish and salty waters. The isolation of these microorganisms has been reported in public water supplies and foods. Some species can be pathogenic to humans, causing gastroenteritis and other infections. Aeromonas isolates from different sources express resistance to antimicrobials, especially -lactams, due to the presence of lactamase enzymes. The pathogenicity of the species is due to the multifactorial virulence, wich includes the production of enterotoxins (Act, Alt and Ast) of Elastase and presense of flagello, among others. Objectives: Identify and quantify Aeromonas hydrophila isolated from treated wastewater and sludge, to investigate the occurrence of virulence genes and resistance to -lactams. Material and methods: The detection and quantification of A. hydrophila were made through the membrane filter technique and specific culture medium, the identification was performed by PCR using a pair of primers specific for the species. After confirming the species sensitivity was performed to know the profile of antibiotic resistance, the survey of virulence genes act, alt, ast, ela, lip, fla and resistance to -lactams gene was performed by PCR and sequencing. Results: We analyzed 15 samples (six of nine treated wastewater and sludge). Of these only nine were positive for A. hydrophila, resulting in 441 typical colonies, of wich 348 were positive by PCR to identify the genus and 209 for species identification. The 209 isolates, being 92 and 117 of treated wastewater and treated sludge showed the following values in the study of the virulence genes: 36 per cent (act), 78 per cent (alt), 82 per cent (fla), 86 per cent (lip), 87 per cent (ela) and 100 per cent of the isolates had at least one of the genes. For antibiotic susceptibility testing all isolates were resistant to at least one antibiotic. The production of MBL, ESBL and AmpC enzyme was detected in isolates. It was also found resistance genes cphA, bla TEM and bla MOX, while genes bla VIM , bla IMP , bla and bla FOX CTX-M were not detected. Conclusion: The results suggest that A. hydrophila can resist the process of treating of wastewater and sludge, moreover, may have different virulence genes and antibiotic resistance, which is why A. hydrophila can be a threat to public health, since these samples are reused for agricultural or urban purposes. , bla SHV

Aeromonas hydrophila is distributed widely in nature and is responsible for an array of human infections. Several studies on the isolation and characterisation of the organism abound. Although there are reports on the antibiotic resistance profiles of the organism, these reports have not been updated in Limpopo province, South Africa despite the established fact that antibiograms vary with time and geographical area. Antibiotic resistance and pathogenesis of an organism are dependent on a host of factors such as the production of extended spectrum beta-lactamases and the genetic profiles such as the genes coding for resistance and possession of integrons and how these characteristics overach with the phylogenetic inter-relatedness of isolates from different sources. In spite of the aforementioned concerns on the efficacy of antibiotics due to the acquisition or endowment of microorganisms with intrinsic and extrinsic factors , which enhances resistance to antibiotics , medicinal plants are reportedly offering promise as alternative sources of efficacious management of infections. Medicinal plants are employed by traditional healers in the management of infections in developing countries especially in Africa. However, the antimicrobial activities of medicinal plants against Aeromonas hydrophila have received only a cursory attention. In an endeavour to undertake a comprehensive study on the isolation, characterisation, antibiograms, activities of medicinal plants as well as the genetic profiles, including phylogenetics relatedness of Aeromonas isolates from different sources, stool and water samples were collected over a two year period from designated places in Limpopo Province and analysed using standard techniques applicable to the constituent research activity. The research findings are presented in six chapters as presented hereunder. The first chapter focussed on the literature review of the organism and reflects areas such as the morphology, laboratory diagnosis, clinical manifestations, pathogenesis, antimicrobial susceptibility profiles, antibacterial activities of medicinal plants as well as the genetic aspects of Aeromonas hydrophila. / Environmental Science / D.Phil. (Environmental Science)

nÃo hà / A descarga de efluentes das indÃstrias tÃxteis para corpos aquosos Ã, correntemente, uma das maiores preocupaÃÃes dos ambientalistas em funÃÃo dos corantes sintÃticos usados para colorir os tecidos poluindo assim o ambiente. A aplicaÃÃo de tratamentos biolÃgicos, sobretudo com a utilizaÃÃo de bactÃrias, apresenta-se como um dos mais viÃveis economicamente, sendo um dos sistemas mais utilizados para descolorir efluentes coloridos. Neste sentido, estudos foram realizados testes para a remoÃÃo de cor dos corantes Remazol Brilliant Blue R, Orange G e Orange II utilizando cepas de Escherichia coli e de Aeromonas hydrophila, isoladas e em cultura mista. Primeiramente foi feito o isolamento das cepas bacterianas de trÃs ambientes diferentes. Em seguida, foram feitos testes para verificar qual concentraÃÃo do corante seria limite para o crescimento de cada microrganismo. AlÃm dos testes de descoloraÃÃo tambÃm foram monitorados outros parÃmetros como o pH, biomassa, remoÃÃo de DQO, proteÃnas totais e toxicidade dos metabÃlitos formados. A cepa Escherichia coli, isolada do ambiente marinho, foi capaz de descolorir concentraÃÃes de 2, 5 e 2 mg L-1, respectivamente, para os corante RBBR, Orange G e Orange II, enquanto que a cepa E. coli, isolada do efluente tÃxtil, descoloriu nas concentraÃÃes de 5, 0,5 e 5 mg L-1, respectivamente. A bactÃria Aeromonas hydrophila descoloriu respectivamente nas concentraÃÃes de 10, 5 e 5 mg L-1, enquanto que o consÃrcio das trÃs bactÃrias descoloriu na concentraÃÃo de 5 mg L-1 para os trÃs corantes testados individualmente. Nessas condiÃÃes de cultivo a diminuiÃÃo na taxa de DQO variou entre 45 e 69%, com a menor taxa observada no ensaio contendo A. hydrophila e o corante Orange II (45%) e a maior taxa de remoÃÃo no ensaio contendo o consÃrcio e o corante RBBR (69%). Bioensaios utilizando o microcrustÃceo Artemia salina mostraram que durante o processo de descoloraÃÃo foram produzidos metabÃlitos com caracterÃsticas recalcitrantes. Os resultados demonstram que as bactÃrias Escherichia coli e Aeromonas hydrophila apresentam potencial biotecnolÃgico na descoloraÃÃo de corantes tÃxteis, desde que sejam utilizadas baixas concentraÃÃes dos corantes / The discharge of effluents from textile industries for water bodies is currently a major concern for environmentalists as a function of synthetic dyes used to color fabrics thus polluting the environment. Biological treatments, especially with the use of bacteria, present themselves as the most economically viable and widely used to decolorize colored effluents. Thus, studies were conducted to test the color removal of dyes Remazol Brilliant Blue R, Orange G and Orange II using isolated and in mixed culture strains of Escherichia coli and Aeromonas hydrophila. Firstly, the isolation of bacterial strains from three different environments was made. Then, tests were performed to verify that the dye concentration would limit the growth of each microorganism. In addition to tests of decolorization, other parameters such as pH, biomass, COD removal, total protein and toxicity of metabolites were also monitored. The Escherichia coli strain isolated from the marine environment was able to decolorize concentrations of 2, 5 and 2 mg L-1, respectively, for the RBBR dye, Orange G and Orange II dyes, while the strain E. coli isolated from textile effluent, decolorized in concentrations of 5, 0.5 and 5 mg L-1, respectively. The bacteria Aeromonas hydrophila decolorized, respectively, at 10, 5 and 5 mg L-1, while the consortium of three bacteria decolorized at concentration of 5 mg L-1 for the three dyes tested individually. In these culture conditions the decrease in the rate of COD ranged from 45% to 69% with the lowest rate observed in the assay containing A. hydrophila and dye Orange II (45%) and the highest removal rate in the test containing the dye RBBR and the consortium (69%). Bioassays using Artemia salina showed that during the process of decolorization metabolites were produced with recalcitrant characteristics. The results show that the bacteria Escherichia coli and Aeromonas hydrophila have biotechnological potential in textile dyes, provided that they use low dye concentrations decolorizing

In Southeast Asia, the family Pangasiidae is important for commercial fisheries and aquaculture. Pangasianodon hypophthalmus (striped catfish) is the most economically important species farmed in Vietnam, with a total export value of 1.7 billion USD in 2012. Intensive aquaculture can lead to problems with major outbreaks of disease and Edwardsiella ictaluri and Aeromonas hydrophila represent two important bacterial pathogens in P. hypophthalmus aquaculture. Immunostimulants have proven to be a very useful food additive for the aquaculture industry, since they can be easily fed to fish to enhance their immune response at times of stress and to improve resistance to disease. The immune system of pangasius catfish has not been fully described, despite the recent growth in aquaculture for this species, and little is known about the effects of immunostimulants on disease resistance. Understanding the immune response is very important in order to evaluate the health status of the fish and assist in control of disease (including prevention) so that production levels by the aquaculture industry can be sustained. The aims of this thesis were to develop and standardise methods to elucidate and measure immune responses in P. hypophthalmus and then to use these with relevant disease models (A. hydrophila and E. ictaluri) and immunomodulators (β-glucans from different sources and at different doses) to determine if bacterial diseases can be controlled, and which functional immune responses and immune genes could be correlated with disease resistance. As a variety of different species from family Pangasiidae are economically important for aquaculture, initial work focused on the characterisation of the immunoglobulin IgM molecule in these species, and anti-P. hypophthalmus IgM mAbs were tested to determine if they cross-reacted between different Pangasiidae species (Chapter 2). Although affinity purification of IgM from the different fish species resulted in a purer preparation ammonium sulphate precipitation (14% w/w), the latter proved faster and easier to perform. The heavy (H) and light (L) chains of IgM from P. hypophthalmus were estimated to be 70-72 kDa and 25-26 kDa, respectively, using SDS-PAGE (12.5%). The L chains of IgM in the other Asian fish species examined were similar in molecular weight to P. hypophthalmus, while the H chains varied (P. gigas and P. larnaudii 76kDa, P. sanitwongsei 69kDa, H. filamentus 73kDa, P. borcoti and H. wyckioides 75kDa, C. bactracus 74kDa, C. macrocephalus 73kDa and C. carpio 70kDa), as did the native IgM molecules. Sedimentation velocity ultracentrifugation was used to determine the molecular weight of the whole IgM molecule from P. hypophthalmus as an alternative to the more commonly used native gels that are run under non-denaturing conditions, although this technique proved more complex. Anti–P. hypophthalmus IgM monoclonal antibodies (mAbs) cross reacted with all of the Pangasiidae species and were successfully applied in an enzyme-linked immunosorbent assay (ELISA) using mAb 23 to measure serum antibody response of P. hypoophthalmus following experimental infection with A. hydrophila by interperitoneal (I.P.) injection in Chapter 3 and E. ictaluri by immersion in Chapter 4. As P. hypophthalmus is a relatively new aquaculture species, there are few reports evaluating its immune response to pathogens. Thus, functional assays were standardised to evaluate both innate and adaptive immune responses of this species and then these assays used to compare immune response following stimulation with live and killed A. hydrophila. (Chapter3). Four treatment groups of 40 fish per group (53.2 ± 14.8g.) consisting of an untreated control group, a group injected I.P. with adjuvant (Montanide ISA 760 VG) only, a group injected with heat-killed A. hydrophila (1 x109 cfu ml-1 mixed with adjuvant), and a group injected with a subclinical dose of live A. hydrophila 2.7 x105 cfu ml-1 were used in the study. Samples were collected 0, 1, 3, 7, 14 and 21 days post injection (d.p.i.) to assess the immune response of fish. The results indicated that challenge with live or/and dead bacteria stimulated the immune response in P. hypophthalmus significantly above control groups with respect to specific antibody titre, lysozyme activity, phagocytosis and plasma peroxidase at 7 or/and 14 d.p.i. Moreover, on 21 d.p.i. total IgM, specific antibody titre and lysozyme activity from both live and dead A. hydrophila challenge groups were significantly different to the control groups. Differential immune responses between live and dead bacterial challenges were also observed as only live A. hydrophila significantly stimulated WBC counts and plasma peroxidase at 3 d.p.i. with the greatest increase in WBC counts noted at 21 d.p.i. and in phagocytosis at 14 d.p.i. By 21 d.p.i. only the macrophages from fish challenged with dead A. hydrophila showed significantly stimulated respiratory burst activity. Immunostimulants are food additives used by the aquaculture industry to enhance the immune response, and β-glucan is now commonly used for this purpose in aquaculture. In Chapter 4 the effect of the prebiotic β-glucan on the immune response and disease resistance of P. hypophthalmus was evaluated. The fish (60.3 ± 11.7 g.) were fed with a basal diet (control) or diets supplemented with fungal derived β-glucan at concentrations of 0.05 %, 0.1 %, or 0.2 % g/kg for four weeks. Fish fed 0.1 % commercial yeast derived β-glucan were also included as a positive control group. Samples were collected from fish on Days 0, 1, 3, 7, 14, 21 and 28. The results showed that fish fed with the highest two levels of fungal derived β-glucan had enhanced immune responses compared to the control group, with respiratory burst activity on all days examined and lysozyme activity on 7 days post feeding (d.p.f.) being significantly elevated (P<0.05) in the group fed with 0.2 % fungal derived β-glucan, while plasma anti-protease activity on 21 d.p.f., natural antibody titre on 3 d.p.f. and complement activity 7 d.p.f. and 14 d.p.i. were significantly enhanced (P<0.05) in the group fed 0.1 % fungal derived β-glucan. The lowest dose of fungal derived β-glucan (0.05 %) appeared insufficient to effectively stimulate the fish’s immune response. WBC count, respiratory burst, lysozyme activity and complement were useful as an early indication of immunostimulation (1 to 7 days). Four weeks after feeding with the different diets, the fish were experimentally infected with E. ictaluri by immersion using 8 x104 cfu ml-1 for 1 h and mortalities were monitored for 14 days. There was a great deal of variation in the level of mortalities within the four replicate tanks for each dietary group. Although the in vivo challenge results showed no statistical differences between the groups fed on the different diets, the highest mortalities were observed in group fed with the control diet and the lowest mortalities were observed in the groups fed with commercial yeast derived β-glucan and 0.2 % fungal derived β glucan. Immune gene expression following stimulation with β-glucan and challenge with E. ictaluri was investigated in Chapter 5.