• Journal of fish pathology
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• v.6 no.2
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• pp.197-204
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• 1993

Flounder culture has been developed mainly in the western parts of japan, and, to date, following six bacterial diseases have been reported. Bacterial white enteritis occurs in 16 to 30-day-old flounder larvae and often causes mass mortality in seed production. Bacterium named Vibrio sp. INFL invades and multiplies in the mucosae of posterier part of intestine, and causes desquamative enteritis. Gliding bacterial disease occurs mostly in juvenile stage and in spring to summer. Diseased signs are partial discoloration and erosion of skin and fins. Histologically, epidermis are removed, and the causative bacterium, Flexibacter maritimus, multiplies on the surface of demis and invades into the muscular tissue. Vibriosis caused by Vibrio anguillarum and related organisum is one of the well-known diseases among marine fish. Outbreaks of the disease in flounder culture are relatively few, but mass mortalities in fingerlings due to the disease were reported. An outbreak of nocardiosis in the autumn of 1984 has been reported, but since then the disease scarcely occurred. The disease is characterized by formation of abscesses under the skin and white nodes in the gill, heart, spleen and kidney. Streptococcicosis occurs frequently in recent years. Beta-hemolytic streptococcus is the causative bacterium, which possesses the same biochemical and serological characteristics as $\beta$-streptococci isolated from some marine and freshwater fish, and is seemed to related to Streptococcus iniae. Edwardsiellosis is the disease that causes most damage in flounder culture in Japan. Characteristic symptoms are swelling of abdomen and intestinal protrusion from the anus due to accumulation of ascites. Edwardsiella tarda, a well-known pathogen of freshwater fish, is the causative bacterium of the disease.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.51 no.4
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• pp.450-455
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• 2018

We examined correlations of the density of fish farms with the distributions of indicator bacteria (Escherichia coli, fecal streptococci) and a bacterial fish pathogen (Streptococcus parauberis) off the coastline of Jeju Island. Seawater samples were collected at four coastal sites on the Island [Aewol (control), Gujwa, Pyoseon and Daejeong] in June, August and October 2016. The indicator bacteria were generally more frequently isolated from samples taken in August when water temperatures and human activities on nearby beaches were highest. Although fish farms were least common at Daejeong, the numbers of isolated fecal indicator bacteria were highest in the seawater and effluent water collected from this site. Hence, fish farms were not likely major contributors of indicator bacteria at Daejeong. We found discrepancies between the isolated bacterial counts and the predicted bacterial copy numbers deduced from our qPCR results, indicating that this pathogen may exist in a viable but non-culturable (VBNC) state in seawater. Thus, livestock wastewater and chemical fertilizer loading off Jeju Island may negatively impact seawater quality more than the effluent released from fish farms does.

• Fisheries and Aquatic Sciences
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• v.19 no.6
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• pp.28.1-28.7
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• 2016

Background: Significant increases in the bacterial resistance to various antibiotics have been found in fish farms. Non-antibiotic therapies for infectious diseases in aquaculture are needed. In recent years, light-emitting diode technology has been applied to the inactivation of pathogens, especially those affecting humans. The purpose of this study was to assess the effect of blue light (wavelengths 405 and 465 nm) on seven major bacterial pathogens that affect fish and shellfish important in aquaculture. Results: We successfully demonstrate inactivation activity of a 405/465-nm LED on selected bacterial pathogens. Although some bacteria were not fully inactivated by the 465-nm light, the 405-nm light had a bactericidal effect against all seven pathogens, indicating that blue light can be effective without the addition of a photosensitizer. Photobacterium damselae, Vibrio anguillarum, and Edwardsiella tarda were the most susceptible to the 405-nm light (36.1, 41.2, and $68.4J\;cm^{-2}$, respectively, produced one log reduction in the bacterial populations), whereas Streptococcus parauberis was the least susceptible ($153.8J\;cm^{-2}$ per one log reduction). In general, optical density (OD) values indicated that higher bacterial densities were associated with lower inactivating efficacy, with the exception of P. damselae and Vibrio harveyi. In conclusion, growth of the bacterial fish and shellfish pathogens evaluated in this study was inactivated by exposure to either the 405- or 465-nm light. In addition, inactivation was dependent on exposure time. Conclusions: This study presents that blue LED has potentially alternative therapy for treating fish and shellfish bacterial pathogens. It has great advantages in aspect of eco-friendly treating methods differed from antimicrobial methods.

• Journal of fish pathology
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• v.35 no.2
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• pp.205-214
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• 2022

In recent years, there have been many studies investigating changes in animal behavior using video tracking technology to track motion. However, there have been very few studies and results on changes in the behavior of fish infected with a pathogen. Therefore, the present study attempted to analyze the behavior of angelfish (Pterophyllum scalare) infected with bacterial pathogens using video tracking. Two cameras were placed in front of the water tank to obtain behavior data, and tracking was performed for three days until the day of death. Data such as average speed, changes in speed, the locations of the fish in the tank, and fractal dimension were statistically analyzed based on the fish speed and location in the tank of the fish. For bacterial infection, an individual angelfish was intraperitoneally injected with approximately 10⁶ CFU ml^-1 of Aeromonas hydrophila or Edwardsiella piscicida. The experiment was carried out five times for each group. Fish infected with the bacterial pathogens showed a tendency to increase in speed and to spend more time in the upper part of the tank one or two days before death. On the day the fish died, the average speed, changes in speed, and the fractal dimension value were significantly lower than the corresponding values in the control group, and the fish also remained in the lower part of the tank. Our results indicated that behavioral changes in fish could be successfully detected earlier than death using video tracking technology, and that this method presents potential for disease monitoring in aquaculture.

• Journal of Microbiology and Biotechnology
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• v.25 no.4
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• pp.511-520
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• 2015

Triclosan, the widely used biocide, specifically targets enoyl-acyl carrier protein reductase (ENR) in the bacterial fatty acid synthesis system. Although the fish pathogen Aeromonas salmonicida subsp. salmonicida exhibits triclosan resistance, the nature of this resistance has not been elucidated. Here, we aimed to characterize the triclosan resistance of A. salmonicida subsp. salmonicida causing furunculosis. The fosmid library of triclosan-resistant A. salmonicida subsp. salmonicida was constructed to select a fosmid clone showing triclosan resistance. With the fosmid clone showing triclosan resistance, a subsequent secondary library search resulted in the selection of subclone pTSR-1. DNA sequence analysis of pTSR-1 revealed the presence of a chromosomal-borne fabV-encoding ENR homolog. The ENR of A. salmonicida (FabVas) exhibited significant homology with previously known FabV, including the catalytic domain YX₍₈₎K. fabVas introduction into E. coli dramatically increased its resistance to triclosan. Heterologous expression of FabVas might functionally replace the triclosan-sensitive FabI in vivo to confer E. coli with triclosan resistance. A genome-wide search for fabVas homologs revealed the presence of an additional fabV gene (fabVas2) paralog in A. salmonicida strains and the fabVas orthologs from other gram-negative fish pathogens. Both of the potential FabV ENRs expressed similarly with or without triclosan supplement. This is the first report about the presence of two potential FabV ENRs in a single pathogenic bacterium. Our result suggests that triclosan-resistant ENRs are widely distributed in various bacteria in nature, and the wide use of this biocide can spread these triclosan-tolerant ENRs among fish pathogens and other pathogenic bacteria.

• Journal of fish pathology
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• v.26 no.3
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• pp.207-217
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• 2013

Recently high mortality of cultured olive flounder, Paralichthys olivaceus occurred frequently at the fish farms in Ulsan, Korea. The diseased fish showed skinny body and swimming behavior around the water surface with liver atrophy and white enteritis as internal signs. The isolated bacteria were identified to V. scophthalmi by biochemical test, nucleotide analysis of 16S rRNA and dnaJ gene sequencing. The pathogen of this study showed strong pathogenicity as 75% mortality to olive flounder by intraperitoneal injection of $1{\times}10^6$ CFU/fish. The pathological sign was not different between the naturally diseased fish and the artificially infected fish. Histopathological changes were shown to liver atrophy, desquamation of the intestinal mucosa and hyaline droplet like as other previous studies.

• Journal of Microbiology and Biotechnology
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• v.26 no.8
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• pp.1457-1463
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• 2016

Vibrio anguillarum, a devastating pathogen causing vibriosis among marine fish, is prevailing in worldwide fishery industries and accounts for grievous economic losses. Therefore, a rapid on-site detection and diagnostic technique for this pathogen is in urgent need. In this study, two mouse monoclonal antibodies (MAbs) against V. anguillarum, 6B3-C5 and 8G3-B5, were generated by using hybridoma technology and their isotypes were characterized. MAb 6B3-C5 was chosen as the detector antibody and conjugated with quantum dots. Based on MAb 6B3-C5 labeled with quantum dots, a modified dot blot assay was developed for the on-site determination of V. anguillarum. It was found that the method had no cross-reactivity with other than V. anguillarum bacteria. The detection limit (LOD) for V. anguillarum was 1 × 10³ CFU/ml in cultured bacterial suspension samples, which was a 100-fold higher sensitivity than the reported colloidal gold immunochromatographic test strip. When V. anguillarum was mixed with turbot tissue homogenates, the LOD was 1 × 10³ CFU/ml, suggesting that tissue homogenates did not influence the detection capabilities. Preenrichment with the tissue homogenates for 12 h could raise the LOD up to 1 × 10² CFU/ml, confirming the reliability of the method.

• Journal of fish pathology
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• v.30 no.2
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• pp.135-148
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• 2017

Pathogen introductions associated with aquatic invasive species threaten ecosystems and biodiversity worldwide. Bigheaded carps (BHC), including Silver Carp Hypophthalmichthys molitrix, Bighead Carp H. nobilis, and their hybrids, are prolific, invasive pests in central US rivers. However, little is known about pathogen effects on invading BHC or how BHC affect the disease risk profile for native fishes in receiving ecosystems. We therefore conducted, from May 2013-December 2014, a systematic pathogen survey for BHC and native fishes in the Wabash River watershed, Indiana, USA. We found Pseudomonas fluorescens, P. putida, and Salmonella enterica DNA in BHC as well as native fishes, although none of these bacteria were exclusively present in BHC. DNA from other bacterial taxa was detected only in native fishes and Common Carp Cyprinus carpio. No gastrointestinal helminths were detected in BHC, although they were common in most native fishes examined. We also conducted in vitro studies on BHC tissues (skin, gill, fin, and fry) and found high sensitivity to Largemouth Bass virus, viral hemorrhagic septicemia virus, and infectious pancreatic necrosis virus. We conclude that BHC are not heavily burdened by bacteria, viruses and parasites in the invaded study ecosystems, although they do harbor native bacteria and show potential for high sensitivity to endemic viruses.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.3
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• pp.443-450
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• 2020

No established method can be used to select effective antibiotics in antibiotic susceptibility tests for fish bacterial pathogens quickly and accurately. Here, we established the optimal conditions for determining the minimal inhibitory concentration (MIC) of major fish bacterial pathogens (Streptococcus spp., Edwardsiella tarda, Vibrio spp., Aeromonas spp., and Pseudomonas spp.) using the KRAQ1 and CAMPY2 panels. The MIC panel used 18 antibiotics of two types and we conducted experiments to establish the optimal culture medium and temperature for each species. The optimal conditions for incubating Streptococcus spp. were in cation-adjusted Mueller-Hinton broth with TES buffer (CAMHBT) at 28℃, using 5% lysed horse blood (LHB) as recommended by the Clinical Laboratory Standards Institute. For Vibrio spp., the optimal culture conditions were 28℃ in CAMHBT supplemented with 1% NaCl. The optimal conditions for culturing E. tarda, Aeromonas spp., and Pseudomonas spp. were in CAMHBT at 28℃.

• Journal of fish pathology
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• v.37 no.1
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• pp.49-60
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• 2024

A viable but non-culturable (VBNC) state is a survival strategy adopted by bacteria when faced with unfavorable environmental conditions, rendering them unable to grow on nutrient agar while maintaining low metabolic activity. This study explored the impact of temperature and nutrient availability on inducing VBNC state in Edwardsiella piscicida, the most important bacterial fish pathogen, and assessed its pathogenicity at VBNC state. E. piscicida was suspended in filtered sterile seawater and exposed to three different temperatures (4, 10, and 25℃) to induce the VBNC state. Subsequently, the induced VBNC cells were subjected to resuscitation by either raising the temperature to 28℃ or inoculating them in brain heart infusion broth supplemented with 1% NaCl. A propidium monoazide (PMA)-qPCR method was also developed to selectively quantify live (VBNC or culturable) E. piscicida cells. The results showed that the bacteria entered the VBNC state after approximately 1 month at 4℃ and 25℃, and 2 months at 10℃. The VBNC E. piscicida cells were successfully revived within 3 days in a nutrient-rich environment at 28℃, highlighting the significance of temperature and nutrition in inducing and resuscitating the VBNC state. In pathogenicity tests, resuscitated E. piscicida cells exhibited high pathogenicity in olive flounder comparable to cultured bacteria, while VBNC cells showed no signs of infection, suggesting they are unlikely to resuscitate in fish. In conclusion, this study contributes to our understanding of fish pathogen ecology by investigating the characteristics of the VBNC state under varying temperature and nutrition conditions.