• Journal of Microbiology and Biotechnology
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• v.19 no.8
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• pp.765-773
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• 2009

Edwardsiella tarda is a pathogen with a broad host range that includes human and animals. The E. tarda hemolysin (Eth) system, which comprises EthA and EthB, is a noted virulence element that is widely distributed in pathogenic isolates of E. tarda. Previous study has shown that the expression of ethB is regulated by iron, which suggests the possibility that the ferric uptake regulator (Fur) is involved in the regulation of ethB. The work presented in this report supports the previous findings and demonstrates that ethB expression was decreased under conditions when the E. tarda Fur ($Fur_{Et}$) was overproduced, and enhanced when $Fur_{Et}$ was inactivated. We also identified a second ethB regulator, EthR, which is a transcription regulator of the GntR family. EthR represses ethB expression by direct interaction with the ethB promoter region. In addition to ethB, EthR also modulates, but positively, luxS expression and AI-2 production by binding to the luxS promoter region. The expression of ethR itself is subject to negative autoregulation; interference with this regulation by overexpressing ethR during the process of infection caused (i) drastic changes in ethB and luxS expressions, (ii) vitiation in the tissue dissemination and survival ability of the bacterium, and (iii) significant attenuation of the overall bacterial virulence. These results not only provide new insights into the regulation mechanisms of the Eth hemolysin and LuxS/AI-2 quorum sensing systems but also highlight the importance of these systems in bacterial virulence.

• Journal of Microbiology and Biotechnology
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• v.27 no.1
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• pp.112-121
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• 2017

Edwardsiella tarda is a gram-negative pathogenic bacterium in aquaculture that can cause hemorrhagic septicemia in fish. Many secreted proteins have already been identified as virulent factors of E. tarda. Moreover, since virulent phenotypes are based on the expression regulation of virulent genes, understanding the expression profile of virulent genes is important. A quantitative RT-PCR is one of the preferred methods for determining different gene expressions. However, this requires the selection of a stable reference gene in E. tarda, which has not yet been systematically studied. Accordingly, this study evaluated nine candidate reference genes (recA, uup, rpoB, rho, topA, gyrA, groEL, rpoD, and 16S rRNA) using the Excel-based programs BestKeeper, GeNorm, and NormFinder under different culture conditions. The results showed that 16S rRNA was more stable than the other genes at different culture growth phases. However, at the same culture time, topA was identified as the reference gene under the conditions of different strains, different culture media, and infection, whereas gyrA was identified under the condition of different temperatures. Thus, in experiments, the expression of gapA and fbaA in E. tarda was analyzed by RT-qPCR using 16S rRNA, recA, and uup as the reference genes. The results showed that 16S rRNA was the most suitable reference gene in this analysis, and that using unsuitable reference genes resulted in inaccurate results.

• Journal of fish pathology
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• v.18 no.3
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• pp.215-225
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• 2005

The effect of extracellular products (ECPs) prepared from highly virulent Edwardsiella tarda PoKF-000623 on the physiological and the immunological function in the olive flounder, Paralichthys olivaceus was evaluated. The virulence of ECPs on the fish, 5.6 g of average body weight was detected $0.714{\mu}{g}$ g $fish^{-1}$ as $96hr-LD_{50}$ by intraperitonial injection. After intramuscularly injected with 0, 4 and $40{\mu}{g}$ ECPs TEX>$fish^{-1}$ to fish average sized 59.1 g of body weight, the fish were measured the glucose and total protein concentration in sera, and immune activity of kidney macrophage. The fish injected with $40{\mu}{g}$ protein $fish^{-1}$ showed a significant increase in the glucose and total protein concentration in sera. But, the fish were changed in cellular immune response as lowed chemiluminescence response and bactericidal activity of head kidney macrophage. These results were suggested that ECPs of E. tarda could be effect on the physiological and the immunological factors, especially in the function of kidney macrophage concerning to edwardsiellosis infection.

• Journal of Aquaculture
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• v.14 no.2
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• pp.81-87
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• 2001

Antimicrobial activity of the essential oil extracted from plants Artemisia princeps var. orientalis, Thuja orientalis and Chamaecyparis obtusa were tested against selected pathogenic bacteria and fungi of fish. At the concentrations above 500ppm, ingibitory effect of the oil of A. princeps var. orientalis was at its peak against Aeromonas hydrophila ATCC 14715, A. hydrophila CF-2, A. salmonicida ATCC 14174 and A. salmonicida EL-1 but the bacteria Edwardsiella tarda KBF-1, Vibrio anguillarum ATCC19264, V. ordalii ATCC33509 and Streptococcus sp. were insensitive. Likewise, the oil extract of T. orientalis showed the highest inhibitory activity against V. ordalii ATCC33509, E. tarda ECK-1, and E. tarda KBF-1 at 300ppm; however the activity was highest at 500ppm or A. hydrophila ATCC14715, A. hydrophila CF-2, A. salomonicida ATCC14174, A. salmonicida EL-1 and Streptococcus sp. SF-1. With increasing dose of C. obtusa oil, the inhibitory activity became more and more effective against A. hydrophila CF-2, A. salomonicida ATCC14174, E. tarda ECK-1 and Streptococcus sp. SF-1, but A. hydrophila ATCC14174, A. salmonicida EL-1, E. tarda KBF-1, V. anguillarum ATCC19264, V. ardalii ATCC33509 and gram positive bacteria (Streptococcus sp.) were somewhat resistant. A. princeps var. orientalis, T. orientalis and C. obtusa were also tested against Saprolegnia sp. at the oil concentrations of 10, 100, 500, 1,000, 1,500 and 2,000ppm. The inhibitory effect of the oil on the inhibit the mycelial growth of Saprolegnia sp. at 10ppm and completely inhibited at over 500ppm.

• Journal of fish pathology
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• v.32 no.2
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• pp.97-104
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• 2019

The purpose of this study was to investigate the antimicrobial resistance and resistance transfer of Vibrio parahaemolyticus and Morganella morganii isolated from fish products purchased from fish markets in Yeosu April - December 2017. These bacteria were identified by biochemical test and PCR results, and the transfer of antimicrobial resistance was confirmed by the broth mating method. To isolate the transconjugants formed during conjugation, TSA medium containing 50 ㎍/ml of ampicillin (AMP), and 150 ㎍/ml of streptomycin (SM) or 30 ㎍/ml of oxytetracycline (OT) was used. M. morganii isolates showed low susceptibility to AMP, amoxicillin (AML), and colistin (CT), erythromycin, OT, and tetracycline, compared to V. parahaemolyticus resistance to AMP, AML, and CT. The conjugation of V. parahaemolyticus or M. morganii with Escherichia coli resulted in the separation of V. parahaemolyticus and M. morganii showing SM resistance as transconjugants. Meanwhile, Edwardsiella tarda transconjugants showing AMP and AML resistance were obtained from the broth mating of V. parahaemolyticus and E. tarda. But the transfer of the VPA0477 which is a β-lactamase gene of V. parahaemolyticus was not confirmed. These results suggest that resistance transfer between pathogenic bacteria is bidirectional and progresses in a wide variety of patterns.

• Journal of fish pathology
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• v.20 no.3
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• pp.281-289
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• 2007

We have investigated lysozyme activity and protectivity of starry flounder, Platichthys stellatus against olive flounder pathogenic bacteria, Edwardsiella tarda, Vibrio ichthyoenteri and Streptococcus iniae in varying salinities, water temperatures and stocking density. Starry flounders were susceptible to E. tarda but not V. ichthyoenteri and S. iniae. Under low salinity condition, the lysozyme activity was decreased a little compared to the control but not significant. The physiological and immune activities were normal up to 26 ℃ culture temperature and 100% stocking density; they were compromised from 29℃ and 200%, respectively.

• Journal of fish pathology
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• v.12 no.2
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• pp.83-88
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• 1999

Green tea extract has been suggested to possess properties of collagenase inhibition and antimicrobial effect to fish pathogenic bacteria. Most fish pathogenic bacteria showed collagenase activities of 0.08-0.7 unit/ml. Among them, Edwardsiella tarda produced large amount of collagenase in the ST medium at $25^{\circ}C$ after 16 hrs. Biosynthesis of the enzyme from E. tarda was decreased to 1/3 by addition of 0.08-0.8 mg/ml of tea extract in the culture medium. The collagenase activity was inhibited almost 100% in the reaction mixture by 0.2 mg/ml of the extract. Then, the minimal inhibition concentration against E. tarda growth appeared as 8 mg/ml of the tea extract in the culture medium.

• Journal of Aquaculture
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• v.16 no.2
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• pp.118-123
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• 2003

This study was conducted to investigate the disinfection effects of chlorine dioxide ($ClO_2$) on 4 fish pathogenic bacteria (Vibrio anguillarum, Edwardsiella tarda, Streptococcus sp. and Staphylococcus sp.) isolated from infected olive flounders. The bacteria were exposed to different concentrations of ClO$_2$ (0.129, 0.246 and 0.455 ppm) and response times (0.5, 1, 3, 5 and 10 min), and then were incubated for 12 hr. The effective disinfection concentrations of $ClO_2$ against experimental bacteria by $ClO_2$ for 0.5 min were observed with 0.455 ppm for Staphylococcus sp., 0.246 ppm for V. anguillarum and E. tarda, and 0.129 ppm for Streptococcus sp., respectively. The duration of exposure at low concentration of $ClO_2$ increased for the disinfectant ability to experimental bacteria.

• Journal of fish pathology
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• v.21 no.3
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• pp.189-199
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• 2008

This paper aims to compare difference with the in an ability of their resistance and survival against in a non-specific defence mechanism of the olive flounder, between the virulent and the avirulent E. tarda strains. The tested E. tarda strains, we divided into the virulent and the avirulent strain groups on the basis of a value of 50% lethal dose (LD50) for the olive flounder weighed 10.3 g in average. The strains of LD50 101.6~104.2 cfu/fish were grouped as virulent strains, such as KE-1, KE-3, KE-5 and FSW910410. The group of avirulent strains as LD50 exceeded 108.7 cfu/fish were included the strains, SU100 and AL92448. A test was conducted to understand the survival ability of each strain in the mucus of the skin and the intestine of olive flounders. The results showed KE-1, KE-3, KE-5 and FSW910410 were highly to survive between 6 hours and 24 hours in intestine. The survival ability in the bile of olive flounder the number of avirulent strains declined during incubation but the virulent strain showed the number of alive bacteria having sustained or increased. In the test for the survival of bacteria in fresh sera of olive flounder, the virulent strains also had tendency to multiply. Concerning the tested bacteria internalization into the head kidney macrophages and the intracellurar replication in the macrophages of olive flounder. The virulent strains exhibited strong internalization, followed high rate replication. According to the results, virulent strains of E. tarda revealed more ability to resist and survive in the face of humoral and cellular defence factors than avirulent strains.

• Journal of fish pathology
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• v.7 no.2
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• pp.113-117
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• 1994

The antimicrobial activity of Artemisia princeps var. orientalis essential oil against a partial fish pathogenic bacteria was examined. The growth of Aeromonas hydrophila, Aeromonas salomonicida, Aeromonas sorbia, Edwardsiella tarda and Streptococcus sp. (yellowtail) were inhibited at concentrations of 1,000 to 2,000 ppm. The A. salmonicida was inhibited at 1,000 ppm, A. hydrophila, A. sorbia, E, tarda and Streptococcus sp. (yellowtail) at 1,500 ppm, but Vibrio anguillarum, Vibrio ordalii, Edwardsiella ictaluri and Streptococcus sp. (SF 1) were grown on 100-2,000 ppm.