• Fisheries and Aquatic Sciences
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• v.18 no.3
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• pp.241-247
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• 2015

In an effort to discover alternative phytotherapeutic antimicrobial agents to combat Streptococcus parauberis, a fish pathogenic bacterium, we evaluated the antibacterial activity of seaweed extracts in vitro. A methanolic extract of Ecklonia cava exhibited strong antibacterial activity against S. parauberis isolated from olive flounder Paralichthys olivaceus. Furthermore, the n-hexane soluble (Hexane) fraction of the E. cava methanolic extract exhibited the greatest antibacterial effect on S. parauberis strains with a minimum inhibitory concentration (MIC) ranging from 256 to $1,024{\mu}g/mL$. In addition, the MIC values of oxytetracycline against antibiotic-resistant S. parauberis were markedly reduced up to 64-fold in combination with the Hexane fraction, suggesting that the antibacterial activity of the antibiotic was restored when combined with the Hexane fraction. The interaction between both antibiotics and the Hexane fraction was assessed by the fractional inhibitory concentration (FIC) index. The Hexane fraction and oxytetracycline combination against antibiotic-resistant S. parauberis strains resulted in a median ${\sum}FIC$ range of 0.502 to 0.516. Thus, the synergistic ranges of median ${\sum}FIC$ < 1 were observed for all combinations of the Hexane fraction and oxytetracycline against S. parauberis. To the best of our knowledge, this is the first report indicating the efficacy of an E. cava extract against fish pathogenic bacterium S. parauberis.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.42 no.5
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• pp.449-455
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• 2009

In Hansan Geojeman area, 2,050 ha of shellfish growing area has been designated as shellfish production area for export. The main shellfish species from the designated area is oysters. For the sanitary management of the designated area established in Hansan Geojeman area, bacteriological examination of sea water and shellfish at the sampling stations inside and outside of the designated area were performed from January 2006 to December 2008. The range of fecal coliform of 756 sea water samples at 21 stations located in the designated area were <1.8~>1,600 MPN/100mL. And the range of geometric mean and the estimated 90th percentile of fecal coliform were 1.8~2.9 and 2.7~15.8 MPN/100mL, respectively. Sanitary conditions of the current designated area in Hansan Geojeman meets the required standards of the Fisheries Product Quality Control and National Shellfish Sanitation Program (NSSP, USA) criteria for the approved area. Also, the sanitary status of the shellfish harvested from the designated area met the Korean Shellfish Sanitation Program (KSSP) fecal coliform criterion (<230 MPN/100g). And the human pathogen such as Salmonella spp. and Shigella spp. were not detected from the examined shellfish samples.

• 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℃.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.3
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• pp.432-442
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• 2020

Diagnostic monitoring in Korean rockfish cages was performed to survey the prevalence of pathogens in cultured Korean rockfish Sebastes schlegeli from May 2013 to July 2016. A total of 1,945 fish samples collected from the western (Cheonsu Bay and Heuksando), southern (Tongyeong and Namhae), and eastern coasts (Pohang) of Korea were tested for parasites, viruses, and bacteria. In this study, 1,264 and 334 fishes were infected with Microcotyle sebastis and Clavinema mariae, respectively. The prevalence rates of C. clavinema in fishes from Cheonsu Bay, Heuksando, and Tongyeong were 35.3%, 3.9% and 1.9%, respectively. No C. clavinema infection was detected in cultured rockfish from Namhae and Pohang. Furthermore, bacteria including Photobacterium damselae (8.9%), Photobacterium piscicola (2.3%), Photobacterium spp. (8.9%), Aeromonas salmonicida (1.8%), Aeromonas spp. (0.9%), Vibrio scophthalmi (1.5%), Vibrio spp. (3.3%), Streptococcus iniae (1.2%), and others (8.0%) were detected in 373 of 1,364 fishes. No virus was detected in any fish investigated in this study.

• Fisheries and Aquatic Sciences
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• v.13 no.2
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• pp.96-101
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• 2010

Norovirus, which causes gastroenteritis in humans, is an important food-borne pathogen worldwide. In an effort to discover an antiviral substance against norovirus, extracts from several seaweeds were evaluated for antiviral activity against feline calicivirus (FCV), which was used as a surrogate. The methanolic extract of Undaria pinnatifida exhibited the most significant antiviral activity and virucidal efficacy against FCV. The concentrations of the extract that reduced viral replication by 50% ($EC_{50}$) and resulted in the death of 50% of the host cells ($CC_{50}$) were 0.05 mg/mL and 1.02 mg/mL, respectively. The selectivity index, calculated from the ratio of the $CC_{50}$ and $EC_{50}$ was 20.4. No FCV infection of host cells occurred following a 1-h incubation in the presence of 12.50 mg/mL U. pinnatifida extract, indicating that the virus was completely inactivated by the extract treatment. The results obtained in this study will contribute to the development of a natural antiviral substance that will prevent food-borne disease caused by norovirus.

• Fisheries and Aquatic Sciences
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• v.14 no.4
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• pp.347-354
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• 2011

Aeromonas salmonicida is an important fish pathogen commonly associated with furunculosis in salmonids. Typical A. salmonicida strains have the surface virulence A-layer protein, a major virulence determinant encoded by the vapA gene. In this study, 880 chum salmon Oncorhynchus keta were collected from the east coast of Korea during 2006-2011, including 560 wild adults and 320 artificially hatched fry pools, and the presence of typical A. salmonicida was examined by PCR using the typical A. salmonicida-specific vapA gene primers. The results demonstrated that 34.5% of the samples (304/880 samples) were PCR positive, implying that a typical A. salmonicida infection is highly prevalent among chum salmon in Korea. Twenty typical A. salmonicida isolates were recovered based on their brown pigmentation on Trypticase Soy Agar (TSA) plates, which indicates the existence of the A-layer protein. Further biochemical analyses with the four randomly selected typical A. salmonicida isolates revealed some variations in their amino acid decarboxylation and carbohydrate fermentation activity. A phylogenetic analysis based on the entire vapA gene sequence suggested that the A. salmonicida isolates from chum salmon were clustered with those isolated from Atlantic salmon in Europe. Further study is needed to resolve such an interesting relationship in detail.

• Journal of fish pathology
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• v.28 no.1
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• pp.1-7
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• 2015

In 2009 outbreaks of an emerging disease in shrimp farms were first reported in China. The disease was known as early mortality syndrome (EMS), or acute hepatopancreatic necrosis disease (AHPND). Since 2009, the disease has been spread to Vietnam, Malaysia, Thailand and Mexico. The causative agent of the disease was identified as Vibrio parahaemolyticus. It is a common seawater inhabitant bacterium, and the pathogen can sometimes contaminate seafood. The disease has caused mass mortality of cultivated shrimp, and huge economic losses in the countries named above. In order to prevent the introduction and establishment of AHPND, emergency measures, such as strengthening of import conditions and even import bans, were put in place by many other countries. In Korea, on the other hand, there are large quantities of shrimp imports from countries, such as Thailand and Vietnam. Transportation of live and fresh dead shrimp is highly likely, and could be a transmission pathway if the shrimp are sourced from populations in AHPND endemic areas. It is important to recognize that importing countries may provisionally adopt sanitary or phytosanitary measures on the basis of available pertinent information, including that from the relevant international organizations, as well as from sanitary or phytosanitary measures applied by other countries based on "Agreement on Application of Sanitary and Phytosanitary Measures". It is pertinent that Korea also takes proper emergent measures to keep out diseases and provide safe seafood.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.48 no.3
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• pp.346-353
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• 2015

Glucocorticoids (GCs) are steroid hormones regulated through responses to stress to maintain diverse metabolic and homeostatic functions. GCs act on the glucocorticoid receptor (GR), a member of the nuclear receptor family. This study identified and characterized the GR gene from the big-belly seahorse Hippocampus abdominalis designating it HaGR. The open reading frame of the HaGR cDNA was 2,346 bp in length, encoding a 782-amino-acid polypeptide with a theoretical isoelectric point of 6.26 and predicted molecular mass of 86.8 kDa. Nuclear receptors share a common structural organization, comprising an N-terminal transactivation domain, DNA-binding domain, and C-terminal ligand-binding domain. The tissue-specific mRNA expression profile of HaGR was analyzed in healthy seahorses using a qPCR technique. HaGR mRNA was expressed ubiquitously in all of the tissues examined, with the highest expression levels in kidney, intestine, stomach, and gill tissues. The mRNA expression in response to immune challenge with lipopolysaccharide (LPS), polyinosinic:polycytidylic acid (poly I:C), Edwardsiella tarda, and Streptococcus iniae revealed that it is inducible in response to pathogen infection. These results suggest that HaGR is involved in the immune response of the big-belly seahorse.

• Journal of Life Science
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• v.17 no.1 s.81
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• pp.162-165
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• 2007

Brown Ring Disease (BRD) is a bacterial disease caused by Vibrio tapetis which affects cultured clam Ruditapes philippinarum and causes heavy economic losses on Atlantic coasts of france, Spain and England. In this study, to evaluate the effective detection of the pathogen, specific primer set based on 16S ribosomal RNA (rRNA) sequences designed for rapid detection of V. tapetis. Polymerase chain reaction (PCR) with this primer set produced the specific band for each V. tapetis. The length of PCR product using designed primer set of Vbts-F and Vbts-R was about 400 bp. Therefore, these primers will be provided with a basic tool for rapid detection of V. tapetis in the various cases such as examination of imported aquatic products, diagnosis of aquatic organisms, and etc.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.36 no.6
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• pp.654-660
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• 2003

To evaluate the biological diversity of fish pathogenic streptococci, 35 strains isolated from diseased olive flounder (Paralichtys olivaceus), were analyzed using a random amplified polymorphic DNA (RAPD) technique with the oligonucleotide commercial primer 6 (Amersham Biosciences). Api 20 Strep test, drug resistance and artificial infection were carried out for further characterization of the isolates. RAPD fingerprints showed similar pattern in 25 strains (about $71.4\%$ of 35 isolates) and these strains were designed as RA group 1. Similarities greater than $44\%$ were obtained when the Dice coefficient was applied among the isolates of RA 1. On the other hand, the reference Streptococcus iniae showed a similar RAPD profile to the isolates with similarity levels of $40-93.3\%.$ Rh I was suggested to be the dominant group isolated from olive flounder suffering from streptococcosis. However, the isolates of Rh 1 group were not classified into the same species by the Api 20 Strep identification system. There was no peculiarity in drug resistance patterns of Rh I group isolates against 7 antibacterial agents. However, only 3 of 25 isolates $(0.12\%)$ showed oxytetracycline (OTC) resistance and OTC might be a useful chemotherapeutic agent in controlling the streptococcosis by strains of RA I group in olive flounder. Fish injected intraperitoneally with $10^5$ CFU of an isolate of Rh I and RA III group showed $60\%\;and\;50\%$ accumulative mortality for 20 days, respectively ($20\%$ in control or Rh II). However luther comparative studies about differences in virulence between isolates are needed.