• Fisheries and Aquatic Sciences
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• v.25 no.5
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• pp.287-297
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• 2022

The objective of this study was to evaluate the probability of norovirus foodborne illness by raw oyster consumption. One hundred fifty-six oyster samples were collected to examine the norovirus prevalence. The oyster samples were inoculated with murine norovirus and stored at 4℃-25℃. A plaque assay determined norovirus titers. The norovirus titers were fitted with the Baranyi model to calculate shoulder period (h) and death rate (Log PFU/g/h). These kinetic parameters were fitted to a polynomial model as a function of temperature. Distribution temperature and time were surveyed, and consumption data were surveyed. A dose-response model was also searched through literature. The simulation model was prepared with these data in @RISK to estimate the probability of norovirus foodborne. One sample of 156 samples was norovirus positive. Thus, the initial contamination level was estimated by the Beta distribution (2, 156), and the level was -5.3 Log PFU/g. The developed predictive models showed that the norovirus titers decreased in oysters under the storage conditions simulated with the Uniform distribution (0.325, 1.643) for time and the Pert distribution (10, 18, 25) for temperature. Consumption ratio of raw oyster was 0.98%, and average consumption amount was 1.82 g, calculated by the Pert distribution [Pert {1.8200, 1.8200, 335.30, Truncate (0, 236.8)}]. ₁F₁ hypergeometric dose-response model [1 - (1 + 2.55 × 10^-3 × dose)^-0.086] was appropriate to evaluate dose-response. The simulation showed that the probability of norovirus foodborne illness by raw oyster consumption was 5.90 × 10^-10 per person per day. The annual socioeconomic cost of consuming raw oysters contaminated with norovirus was not very high.

• Journal of Food Hygiene and Safety
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• v.35 no.1
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• pp.37-44
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• 2020

This study investigated the probability of foodborne illness caused by raw oyster consumption contaminated with high risk Vibrio species such as V. vulnificus and V. cholerae. Eighty-eight raw oyster samples were collected from the south coast, west coast and Seoul areas, and examined for the prevalence of high risk Vibrio species. The growth patterns of V. vulnificus and V. cholerae in raw oysters were evaluated, and consumption frequency and amounts for raw oyster were investigated from a Korean National Health and Nutrition Examination Survey. With the collected data, a risk assessment simulation was conducted to estimate the probability of foodborne illness caused by intake of raw oysters, using @RISK. Of 88 raw oysters, there were no V. vulnificus- or V. cholerae-positive samples. Thus, initial contamination levels of Vibrio species in raw oysters were estimated by the statistical methods developed by Vose and Sanaa, and the estimated value for the both Vibrio spp. was -3.6 Log CFU/g. In raw oyster, cell counts of V. vulnificus and V. cholerae remained unchanged. The incidence of raw oyster consumers was 0.35%, and the appropriate probabilistic distribution for the consumption amounts was the exponential distribution. A risk assessment simulation model was developed with the collected data, and the probability of the foodborne illness caused by the consumption of raw oyster was 9.08×10^-15 for V. vulnificus and 8.16×10^-13 for V. cholerae. Consumption frequency was the first factor, influencing the probability of foodborne illness.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.50 no.2
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• pp.120-129
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• 2017

This study assessed the safety of raw oysters Crassostrea gigas for consumption during processing in a processing plant. Bacterial contamination (e.g., viable cell counts, coliform groups, Escherichia. coli and pathogenic bacteria) and chemical contamination (e.g., heavy metals and shellfish toxins) were measured on raw oysters, a processing equipment, employees and work areas. No total mercury, lead, paralytic shellfish poison, diarrheic shellfish poison or norovirus was detected in any post-harvested oyster samples. However, the cadmium level ranged from 0.1-0.2 mg/kg. The viable cell count, E. coli and coliform group levels in post-harvested oysters ranged from 4.00-4.54 log CFU/g, ND-210 MPN/100 g and 110-410 MPN/100 g, respectively. The viable contaminating cell counts on employees, equipment and work areas were in the range of $0.90-3.46log\;CFU/100cm^2$. Airborne bacteria in the work areas ranged from 0.60 to 1.81 log CFU/plate/15 min. Thus, no significant health risks were detected in the processing plant.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.50 no.4
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• pp.335-342
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• 2017

Oysters Crassostrea gigas are a globally popular shellfish for human consumption. As filter-feeding bivalve mollusks, oysters may harbor many microorganisms and chemicals that could pose potential human health risks. The objective of this study was to investigate the suitability of cultured oysters for raw consumption or use in seafood products by measuring concentrations of harmful microorganisms and chemicals in their flesh. Microbial concentrations in cultured oysters were found to be: $1.0{\times}10^2-6.0{\times}10^4CFU/g$ (viable cell counts), not detected $(ND)-5.4{\times}10^3CFU/g$ (coliform bacteria), $ND-1.3{\times}10^2CFU/g$ (E. coli), and $ND-4.6{\times}10^3CFU/g$ (Vibrio parahaemolyticus). Other pathogenic bacteria, including Enterohemorrhagic E. coli (EHEC), Listeria monocytogenes, Staphylococcus aureus, and Salmonella spp., were not detected in any samples. Heavy metal concentrations of cultured oysters were ND-0.239 mg/kg (total mercury), ND-1.091 mg/kg (lead), ND-0.968 mg/kg (cadmium). The concentrations of benzo(a)pyrene ranged from $0.280-0.880{\mu}g/kg$. Paralytic shellfish poison ranged from ND-0.58 mg/kg, while diarrhetic shellfish poison was not detected. No radioactivity was detected. These results suggest that oysters intended for raw consumption or use in seafood products should be subjected to chemical and biological controls.

• Journal of Food Hygiene and Safety
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• v.33 no.4
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• pp.248-254
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• 2018

To assess the risk of V. parahaemolyticus infection caused by consumption of raw oysters in Korea, contamination levels during the retail-to-table route of oysters was modeled to predict V. parahaemolyticus growth based on temperature and time. The consumed amount data of the KNHANES and the standard recipe of RDA were applied. A consumption scenario for exposure assessment was developed and combined with a Beta-Poisson dose-response model. The estimated probability of illness from consumption of pathogenic V. parahaemolyticus in raw oysters during three separate months (April, October, and November) was $5.71{\times}10^{-5}$ (within the 5th and 95th percentile ranges of $2.71{\times}10^{-8}$ to $1.03{\times}10^{-4}$). The results of the quantitative microbial-risk assessment indicated that the major factors affecting the probability of illness were the initial contamination level at the retailer, the consumed amount, the prevalence of pathogenic strains [tdh or trh genes], and exposure temperature and time.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.28 no.3
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• pp.347-353
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• 1995

[ $F_o-value$ ] of canned smoked-oyster in cottonseed oil (SOCO) were measured using a microcomputer aided $F_o-value$ measuring system, and the microbiological safety of the canned SOCO was evaluated to optimize the energy consumption. Most of the microorganisms in raw oyster were saprophytes. No microorganisms were detected from the canned SOCO which was pretreated by conventional procedure and sterilized at $110^{\circ}C$ with $F_o-value$ of 5.92min and over. The most heat resistant microflora isolated from the raw oyster was Bacillus sp.. D-value at $121.1^{\circ}C$ and z-value of spores of Bacillus sp. in the SOCO homogenate were 4.10min and $10,91^{\circ}C$, respectively. After 120 days storage at $50^{\circ}C$, no growth of microorganisms was recognized from the canned SOCO with $F_o-value$of 5.92min.

• Journal of Marine Bioscience and Biotechnology
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• v.2 no.4
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• pp.263-266
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• 2007

Vibrio vulnificusis a causative agent of serious diseases in humans resulting from the contact of wound with seawater or consumption of raw seafood. Several studies aimed at detecting V. vulnificus have targeted vvh as a representative virulence toxin gene belonging to the bacterium. In this study, we targeted the rpoS gene, a general stress regulator, to detect V. vulnificus. PCR specificity was identified by amplification of 8 V. vulnificus templates and by the loss of a PCR product with 36 non-V. vulnificus strains. The PCR assay had the 273-bp fragment and the sensitivity of 10 pg DNA from V. vulnificus. SYBR Green I-based real-time PCR assay targeting the rpoS gene showed a melting temperature of approximately $84^{\circ}C$ for V. vulnificus strains. The minimum level of detection by real-time PCR was 2 pg of purified genomic DNA, or $10^3$ V. vulnificus cells from pure cultured broth and $10^3$ cells in 1g of oyster tissue homogenates. These data indicate that real-time PCR is a sensitive, species-specific, and rapid method for detecting this bacterium using the rpoS gene in pure cultures and in infected oyster tissues.

• Fisheries and Aquatic Sciences
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• v.18 no.3
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• pp.235-240
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• 2015

Seasonal variation in the prevalence of norovirus in oysters Crassostrea gigas was investigated and compared to levels of Escherichia coli, a fecal indicator in oysters. Oysters were collected from Iwon-myeon, Taean-gun, Korea, a primary production area for European Union export of oysters between 2013 and 2014. We observed seasonality in the prevalence of norovirus in oysters, with a higher prevalence and viral load detected during winter months. Oysters taken from production areas that complied with the European Union standard for raw consumption (< 230 MPN/100 g of E. coli) had 22.1% of the samples test positive for norovirus (15/68 samples). However, norovirus was not detected in any of the samples (0%, 0/4 samples) that were collected from production sites that exceeded the standard fecal contamination level for raw consumption (> 230 MPN/100 g of E. coli). These results indicated that there is a negative correlation between the prevalence of norovirus and high levels of E. coli in oysters. Therefore, our results suggest that current food safety guidelines using only a bacterial fecal contamination indicator, E. coli, may not adequately assess shellfish production areas for viral and bacterial contamination.

• Korean journal of food and cookery science
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• v.24 no.6
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• pp.919-930
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• 2008

This study was conducted to survey the attitudes of oyster consumers and to analyze their purchase behaviors based on demographic variables. To accomplish this, a questionnaire that was developed based on content analysis and panel discussion was distributed to 467 general consumers. The majority of the respondents ate oysters (90.6%), although the proportion of oyster consumers increased with age. The primary reasons for not-eating oysters were odor (33.3%), flavor (16.7%) and concern for safety (11.9%). Most respondents consumed raw oysters (96.1%) during winter (70.0%) at discount stores (51.3%). Fishery wholesale markets were the most common places to purchase oysters for respondents in their 60 s, while the other groups reported that discount stores were the most common place to purchase oysters. Most respondents ate oysters the day of purchased (53.2%). Furthermore, most respondents (39.2%) reported that they consumed the oysters only after evaluating the appearance and odor and that they avoided oysters during summer for safety. Women were more likely to check the expiration date than men, while housewives were the most likely to check the expiration and usually kept the oysters at refrigerator. Overall, the results of this study suggest that the various types of oyster products must be targeted toward different demographic markets. Moreover, this study will be useful for promoting the safer and more effective consumption of oysters.

• Journal of Microbiology and Biotechnology
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• v.18 no.11
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• pp.1841-1847
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• 2008

Vibrio vulnificus is a causative agent of serious diseases in humans, resulting from the contact of wound with seawater or consumption of raw seafood. Several studies aimed at detecting V. vulnificus have targeted vvh as a representative virulence toxin gene belonging to the bacterium. In this study, we targeted the rpoS gene, a general stress regulator, to detect V. vulnificus. PCR specificity was identified by amplification of 8 V. vulnificus templates and by the loss of a PCR product with 36 non-V. vulnificus strains. The PCR assay had the 273-bp fragment and the sensitivity of 10 pg DNA from V. vulnificus. SYBR Green I-based real-time PCR assay targeting the rpoS gene showed a melting temperature of approximately $84^{\circ}C$ for the V. vulnificus strains. The minimum level of detection by real-time PCR was 2 pg of purified genomic DNA, or $10^3$ V. vulnificus cells from pure cultured broth and $10^3$ cells in 1 g of oyster tissue homogenates. These data indicate that real-time PCR is a sensitive, species-specific, and rapid method for detecting this bacterium, using the rpoS gene in pure cultures and in infected oyster tissues.