111 research outputs found

    Enviromental factors affecting the pathogenesis of Edwardsiella ictaluri in striped catfish Pangasianodon hypophthalmus (Sauvage)

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    Bacillary Necrosis of Pangasius (BNP) caused by Edwardsiella ictaluri is considered to be the most serious disease occurring in farmed striped catfish (Pangasianodon hypophthalmus) in Vietnam. This disease has had an increasing impact over the last ten years and has been reported to cause 50-90% mortality of stocks during a single outbreak. Data obtained from natural outbreaks of E. ictaluri in striped catfish showed the role of environmental factors in the establishment and progression of this disease. At present, factors affecting the virulence and transmission of E. ictaluri in striped catfish are poorly understood. The central hypothesis of this thesis focuses on the complex picture of the environmental factors and infectivity of E. ictaluri in striped catfish. In this study, 80 isolates of E. ictaluri recovered from natural clinical disease outbreaks occurring in striped catfish farms between 2002 and 2011 located in 4 distinct geographical areas within Vietnam were characterised using a variety of methods. The biochemical profiles showed that E. ictaluri isolates from striped catfish in Vietnam have similar phenotypic characteristics to other E. ictaluri isolates from other infected fish species. These data showed high levels of phenotypic homogeneity between the E. ictaluri isolates investigated. The status of isolates recovered from natural infections over time and from geographically distinct farms was evaluated using pulsed-field gel electrophoresis (PFGE), plasmid profile identification and antibiotic sensitivity tests. The PFGE results showed 6 main groups with a similarity of 82% and the corresponding genotypes of the prevalent isolates illustrated annual differences. Three plasmid groups were identified distributed among the isolates investigated, in which high molecular weight plasmids of approximately 35 and 140 kb were found in two of the groups. Plasmid profiles of the present study did not show any trend of geographical region or year of isolation. The 140 kb plasmid has been considered as a multi-antibiotic resistance plasmid which confers resistance to tetracycline, trimethoprim and sulphonamides. All Vietnamese isolates showed a high level of resistance to Oxolinic acid, Sulfadimethoxine/Ormetoprim (Romet), Oxytetracycline and Amoxicillin. A reproducible bacterial immersion challenge model was developed and the LD60 estimated prior to performing subsequent experimental challenge studies. Fish were exposed to 107 cfu ml-1 of E. ictaluri by immersion for up to 30 seconds, resulting in a cumulative percentage mortality of 63%. Edwardsiella ictaluri was recovered and identified from all the dead and moribund fish during these experiments and affected fish showed similar clinical signs and pathology to those reported from natural E. ictaluri infections. The present study resulted in a successful experimental immersion challenge model for E. ictaluri infection in healthy striped catfish. Cohabitation challenges were also developed and produced 15-40% mortality, typical clinical signs and pathology, and successful recovery of the challenge organism demonstrating horizontal transmission of E. ictaluri in striped catfish. Experimental studies were then conducted to investigate the association between pH or salinity of water and susceptibility to E. ictaluri infection in striped catfish. The first experiments were performed in in vitro conditions in which E. ictaluri isolates were cultured in a variety of pH and salt concentrations. In vivo experiments were then designed where striped catfish were exposed to 107 cfu ml-1 of E. ictaluri for 30 seconds and then held at 4 different water pHs (5.5, 6.5, 7.5 and 8.5) or NaCl concentrations (0, 0.5, 1 and 1.5%). The results of in vitro experiments showed that a pH value between 5.5 to 6.5 and salt concentration between 0-0.5% were optimal for the growth of E. ictaluri. The in vivo experiments demonstrated that the cumulative mortality of striped catfish in water at pH 5 and pH 6 was significantly higher than that of fish maintained in more alkaline water (p<0.05). By contrast, the cumulative mortality of the striped catfish maintained in 0.5% salt concentration was significantly lower than those kept in 0%, 1% and 1.5% salt concentration (p<0.05). Clinical signs, lesions and histopathological changes in the affected fish were consistent with those reported in natural infections. This study highlighted the use of pH 8.5 and salinity of 0.5% NaCl as a means of decreasing the susceptibility of striped catfish to E. ictaluri. In conclusion, this study used a variety of methods in order to enhance the understanding of the biochemical, biophysical characteristics, plasmid profile and antibiotic resistance as well as the relatedness of E. ictaluri isolates recovered from farmed striped catfish in Vietnam. This study provided two reliable and reproducible bacterial challenge models (immersion and cohabitation) and emphasised the link between pH and salinity with the infectivity and pathogenicity of E. ictaluri in striped catfish

    Optimal Number, Location, and Size of Distributed Generators in Distribution Systems by Symbiotic Organism Search Based Method

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    This paper proposes an approach based on the Symbiotic Organism Search (SOS) for optimal determining sizing, siting, and number of Distributed Generations (DG) in distribution systems. The objective of the problem is to minimize the power loss of the system subject to the equality and inequality constraints such as power balance, bus voltage limits, DG capacity limits, and DG penetration limit. The SOS approach is defined as the symbiotic relationship observed between two organisms in an ecosystem, which does not need the control parameters like other meta-heuristic algorithms in the literature. For the implementation of the proposed method to the problem, an integrated approach of Loss Sensitivity Factor (LSF) is used to determine the optimal location for installation of DG units, and SOS is used to find the optimal size of DG units. The proposed method has been tested on IEEE 33-bus, 69-bus, and 118-bus radial distribution systems. The obtained results from the SOS algorithm have been compared to those of other methods in the literature. The simulated results have demonstrated that the proposed SOS method has a very good performance and effectiveness for the problem of optimal placement of DG units in distribution systems

    Accounting Information Security Control and Satisfaction of Accountants Regarding Accounting Information Systems

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    This study analyzes the factors affecting accountants’ satisfaction with the accounting information system in Vietnamese enterprises. The research results of this study show that the factors affecting user satisfaction with the accounting information system are directly influenced by four factors: the quality of the accounting workforce, perception of usefulness, system quality, and information quality. The quality of the accounting workforce is the factor that has the greatest direct impact on the accountant’s satisfaction. The second is the perceived usefulness factor. The third is the system quality factor, and the last is the information quality factor. In particular, the results of this study indicate that humans are an important factor. Knowledge of accounting information security control is directly proportional to accountants’ satisfaction with the accounting information system. The results can be used to recommend enterprises improve accountants’ satisfaction, helping to increase work efficiency. Objectives: The main objectives of this study include: (1) Identifying the factors influencing the satisfaction of accountants with the accounting information system in enterprises in Vietnam. (2) Determining the relationship between accounting information security and the satisfaction of accountants with the accounting information system. (3) Providing recommendations to enhance the satisfaction of accountants with the accounting information system in enterprises in Vietnam. Methods: This study uses qualitative and quantitative research. During the qualitative process, this study analyzed related works. Group discussions are used to provide initial assessments of measurement scales, concepts, and research hypotheses and to adjust, supplement, and explore influencing factors. The questionnaire and the research model are reviewed by the experts. Quantitative research involved data collection through survey investigations based on a designed questionnaire via Google Forms. The formal research survey was conducted using a stratified sampling method, encompassing businesses from various sectors. The quantitative research employed the Cronbach Alpha reliability test for the measurement scales, exploratory factor analysis (EFA), confirmatory factor analysis (CFA), and the use of structural equation modeling (SEM) to assess the structural relationships. Descriptive statistics and tests of significance were also utilized. Findings: The results of the study on the factors affecting user satisfaction with an accounting information system are directly influenced by four factors: system quality, information quality, quality of accountants, and perceived usefulness. The quality of the accounting workforce has the greatest direct impact on the accountant’s satisfaction, followed by perceived usefulness, system quality, and information quality factors. Novelty:This study discovered a relationship between knowledge of accounting information security and the level of satisfaction among accountants regarding information technology systems in enterprises in Vietnam. This finding can assist enterprises in implementing strategies to provide more training on accounting information security for their employees. Doi: 10.28991/ESJ-2023-07-05-06 Full Text: PD

    Environmental conditions influence susceptibility of striped catfish Pangasianodon hypophthalmus (Sauvage) to Edwardsiella ictaluri

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    Over the last 20 years the production farmed Vietnamese striped catfish (Pangasianodon hypophthalmus) has increased significantly and in 2016, over 1.2 million tonnes of catfish were farmed and sold globally. Bacterial disease outbreaks due to Edwardsiella ictaluri continue to be one of the biggest threats to the sector, however, little is known on how the environmental conditions affect the survival of the fish during disease outbreaks. Growth of 14 Edwardsiella ictaluri strains recovered from natural disease outbreaks occurring in 4 provinces in Vietnam between 2002 and 2011 was investigated in vitro under different pH and salt concentrations. The results showed that a pH value of 6.5, NaCl concentration of 0.5% was optimal for the growth of the bacteria in vitro. The effect of varied pH and salt concentrations on the susceptibility of striped catfish to E. ictaluri infection was also studied in vivo following an immersion bacterial challenge (1.1 x 107 cfu ml−1 E. ictaluri for 30 s). The cumulative mortality of striped catfish in water at pH 5.5 and pH 6.5 was significantly higher than that of fish maintained in more alkaline water (p < .05). The cumulative mortality of the striped catfish maintained in 0.5% NaCl was significantly lower than those kept in 0%, 1% and 1.5% NaCl (p < .05). This study identified the effect of pH and salinity changes on the susceptibility of striped catfish to E. ictaluri infections

    Factors impact on the effectiveness of internal control systems in credit facilities in Binh Thuan province commercial banks

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    The study aims to confirm and measure factors that affect the effectiveness of internal control systems in credit facilities in Binh Thuan province commercial banks. This research used the framework by COSO 2013 and results of expert interviews to offer research models and scales. It was carried out for collecting data from 300 managers and employees of 10 commercial banks (30 people/bank) in Binh Thuan province in 2020. The study used a 5-level likert scale and used SPSS 22.0 software for analysis. The results of multivariate regression analysis (OLS) show that all factors: Risk assessment, Risk management, Control environment, Control procedure, Control activities, Credit control, Control capacity , Information, Communicates internally, Communicates externally have an impact on the effectiveness of internal control systems in credit facilities of commercial Banks in Binh Thuan province

    Experimental Evaluation on Engineering Properties and Drying Shrinkage of No-Cement Mortar Produced by Alkaline Activation of Fly Ash-Slag Mixtures

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    Turning locally available industrial by-products such as fly ash (FA) and ground granulated blast-furnace slag (GGBFS) into cement-free materials has been recently received much attention from researchers. Following this trend, the present study produces alkali-activated mortars (AAFS) using a mixture of FA and GGBFS as a precursor activated by an alkaline solution of sodium hydroxide and sodium silicate. Five AAFS mixtures were prepared for the evaluation of engineering properties, drying shrinkage, and microstructural observation using various FA/GGBFS ratios of 30/70, 40/60, 50/50, 60/40, and 70/30. The experimental results show that the proportions of FA and GGBFS significantly affected the performance of the AAFS in both fresh and hardened stages. Higher GGBFS content resulted in a reduction in flowability and higher fresh unit weight. The GGBFS-rich AAFS developed its mechanical strength faster than the FA-rich AAFS and the strength gain of the GGBFS-rich AAFS was significantly higher than that of the cement-based mortar at only 1-day old, confirming the applicability of AAFS as a structural material and its potential to replace cement in the no-cement mortar production. The AAFS sample incorporating 60% of GGBFS and 40% of FA exhibited the highest strength, lowest water absorption, and less drying shrinkage with a relatively dense microstructure among the AAFS samples


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    Amine-SiO2 material was synthesized and applied as a novel adsorbent for nitrate and phosphate removal from aqueous solution. The characterization of Amine-SiO2 were done by using TGA, FTIR, BET, and SEM analyses. Results showed that Amine-SiO2 had higher nitrate and phosphate adsorption capacity of 1.14 and 4.16 times, respectively, than commercial anion exchange resin (Akualite A420). In addition, Amine-SiO2 also had good durability with stable performance after at least 10 regeneration times, indicating that this material is very promising for commercialization in the future as an adsorbent for water treatment

    The Combined Use of Pediococcus pentosaceus and Fructooligosaccharide Improves Growth Performance, Immune Response, and Resistance of Whiteleg Shrimp Litopenaeus vannamei Against Vibrio parahaemolyticus

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    In this study, we evaluated the effect of probiotic bacteria Pediococcus pentosaceus supplemented at different inclusion levels in a control diet [basal diet containing 0.5% fructooligosaccharide (FOS)] on the growth performance, feed conversion ratio, immune response, and the disease resistance of whiteleg shrimp Litopenaeus vannamei juveniles against Vibrio parahaemolyticus. A control diet with 0.5% FOS but without P. pentosaceus supplementation (Control) was prepared. In addition, three other test diets were also formulated: control diet supplemented with P. pentosaceus at (i) 1 x 10(6) cfu g(-1) diet (P1), (ii) 1 x 10(7) cfu g(-1) diet (P2), or (iii) 1 x 10(8) cfu g(-1) diet (P3). After a 60-day feeding trial, the experimental shrimps were challenged with V. parahaemolyticus. The results showed that dietary supplementation of P. pentosaceus significantly improved the growth performance and immune responses of L. vannamei juveniles. The juveniles that were fed with a P2 or P3 diet recorded the maximum increase in the final body weight, final length, weight gain, and survival rate. The total hemocyte counts, phenoloxidase, and lysozyme activity of shrimp fed with either of these two diets were significantly enhanced. The results also showed that juveniles fed with a P2 or P3 diet exhibited significantly lower mortality when challenged with V. parahaemolyticus. Overall results suggested that a combination of P. pentosaceus at the inclusion level of 1 x 10(7) cfu g(-1) diet (P2) and 0.5% FOS could be considered as a potential synbiotic formulation for improving the growth, health, and robustness of L. vannamei

    Gut microbiota of migrating wild rabbit fish (Siganus guttatus) larvae have low spatial and temporal variability

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    We investigated the gut microbiota of rabbit fish larvae at three locations in Vietnam (ThuanAn-northern, QuangNam-intermediate, BinhDinh-southern sampling site) over a three-year period. In the wild, the first food for rabbit fish larvae remains unknown, while the juveniles and adults are herbivores, forming schools near the coasts, lagoons, and river mouths, and feeding mainly on filamentous algae. This is the first study on the gut microbiota of the wild fish larvae and with a large number of individuals analyzed spatially and temporally. The Clostridiales order was the most predominant in the gut, and location-by-location alpha diversity showed significant differences in Chao-1, Hill number 1, and evenness. Analysis of beta diversity indicated that the location, not year, had an effect on the composition of the microbiota. In 2014, the gut microbiota of fish from QuangNam was different from that in BinhDinh; in 2015, the gut microbiota was different for all locations; and, in 2016, the gut microbiota in ThuanAn was different from that in the other locations. There was a time-dependent trend in the north-south axis for the gut microbiota, which is considered to be tentative awaiting larger datasets. We found limited variation in the gut microbiota geographically and in time and strong indications for a core microbiome. Five and fifteen OTUs were found in 100 and 99% of the individuals, respectively. This suggests that at this life stage the gut microbiota is under strong selection due to a combination of fish-microbe and microbe-microbe interactions
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