Survival strategies of Listeria monocytogenes to environmental hostile stress: biofilm formation and stress responses

변계환,김현정 한국식품과학회 2023 Food Science and Biotechnology Vol.32 No.12

Listeria monocytogenes is a critical foodborne pathogen that causes listeriosis and threatens public health. This pathogenicmicroorganism forms a transmission cycle in nature, food industry, and humans, expanding the areas of contamination amongthem and infl uencing food safety. L. monocytogenes forms biofi lms to protect itself and promotes survival through stressresponses to the various stresses (e.g., temperature, pH, and antimicrobial agents) that may be infl icted during food processing. Biofi lms and mechanisms of resistance to hostile external or general stresses allow L. monocytogenes to survive despitea variety of eff orts to ensure food safety. The current review article focuses on biofi lm formation, resistance mechanismsthrough biofi lms, and external specifi c or general stress responses of L. monocytogenes to help understand the unexpectedsurvival rates of this bacterium; it also proposes the use of obstacle technology to eff ectively cope with it in the food industry.

Listeria monocytogenes의 검출을 위한 loop-mediated isothermal amplification, real-time PCR, 배지 도말법의 검출 성능 및 특성 비교

변계환,한상하,최승호,방현조,강성일,김수경,하상도 한국식품저장유통학회 2022 한국식품저장유통학회지 Vol.29 No.3

Listeria monocytogenes is a foodborne pathogen causing listeriosis, which can be fatal in specific high-risk groups. The aim of this study was to compare the performance (accuracy, sensitivity, and specificity) of 3MTM Molecular Detection System (3MTM MDS) and Korean Food Codex [real-time PCR (RT-PCR) and selective agar] for the detection of L. monocytogenes in various food matrices. The detection performance of the three methods was determined against 100-103 CFU/mL of L. monocytogenes in vitro and showed high accuracy in the order of RT-PCR, 3MTM MDS, and selective agar. There was no difference in sensitivity and specificity of the three methods. Eleven food matrices, selected from agricultural, livestock, and seafood products, were artificially inoculated with 100-103 CFU/25 g of L. monocytogenes and enriched in 3MTM Demi-Fraser Broth. None of the three methods could completely detect low concentrations of L. monocytogenes in a food matrix. However, 3MTM MDS, which is a loop-mediated isothermal amplification (LAMP)-based technology for rapid detection, showed a higher positive detection rate than RT-PCR did, but lower than that of selective agar. These data indicated that 3MTM MDS was superior for the rapid detection of L. monocytogenes, compared to RT-PCR in food matrices containing various inhibitors. Consequentially, the study findings suggest that the LAMP method is a promising alternative to RT-PCR for the rapid detection of foodborne pathogens.

즉석섭취식품에 존재하는 Salmonella spp.와 Listeria monocytogenes의 검출을 위한 SureTectTM와 표현형 및 유전자형 방법의 비교

변계환,김병후,조아진,허은,윤성희,김태익,하상도 한국식품저장유통학회 2023 한국식품저장유통학회지 Vol.30 No.2

The objective of this study is to compare and assess the effectiveness of real-time polymerase chain reaction (RT-PCR), loop-mediated isothermal amplification (LAMP), and the selective agar plate method for the detection of Salmonella spp. and Listeria monocytogenes in ready-to-eat (RTE) foods. In RTE foods, the detection performance of the three methods (RT-PCR [SureTectTM kit and PowerChekTM kit], LAMP [3M MDS], selective agar) were similar at 0-10, 10-50, 50-100, and 100- CFU/mL of Salmonella spp. and L. monocytogenes. We found that with RT-PCR, the Ct value of salad was significantly higher (p<0.05) than other RTE foods, indicating that fiber plays a critical role as an obstacle to the rapid detection of Salmonella spp. However, the Ct value displayed a mixed pattern according to the inoculation level of L. monocytogenes. The use of rapid detection kits and machines mostly depends on the user’s choice, with accuracy, ease of use, and economy being the primary considerations. As an RT-PCR kit, SureTectTM and PowerChekTM showed high accuracy in detecting Salmonella spp. and L. monocytogenes in RTE foods, showing that they can replace the existing RT-PCR kits available. Additionally, LAMP also showed excellent detection performance, suggesting that it has the potential to be used as a food safety management tool.

소규모 가공경영체 떡류의 생산과정에 따른 미생물학적 품질조사를 위한 모니터링

한상하,김경준,변계환,김덕현,최송이,하상도,Han, Sangha,Kim, Kyeongjun,Byun, Kye-Hwan,Kim, Duk-Hyun,Choi, Song-yi,Ha, Sang-do 한국식품위생안전성학회 2021 한국식품위생안전성학회지 Vol.36 No.5

편의식 소비가 증가하는 식문화가 정착되면서 쌀의 소비형태가 전통적인 쌀밥에서 편의식 가공제품 형태로 변화되면서 떡류는 훌륭한 대체재로 자리 잡아가고 있다. 하지만 대부분의 떡은 소규모의 영세한 업체에서 제조되고 있으며 구입 후 별도의 조리과정 없이 그대로 섭취하므로 떡의 미생물학적 안전성에 대한 우려가 증가되는 추세이다. 따라서 본 연구는 떡류에서 발생하는 미생물학적 안전성을 개선하고자 소규모 업체의 떡류, 생산 환경 및 작업자의 미생물 오염도를 조사하였다. 3가지 떡(가래떡, 인절미, 경단)을 선정하여 원료, 제조공정 및 제조환경에 대한 미생물 오염도를 측정한 결과, 6가지 원재료에서 일반세균 3.76-4.48, 대장균군 2.21-4.14, B. cereus 1.02-1.15 log CFU/g 수준으로 검출되었고, E. coli는 검출되지 않았다. 떡의 제조공정별 오염도 분석결과, 세척과정 후 원재료의 일반세균, 대장균군 및 B. cereus의 오염도가 감소하였지만 불림, 분쇄공정에서 다시 증가하였고, 증자 후에는 3종류의 떡에서 모두 검출한계 이하의 수준을 보였다. 그러나 증자 이후 성형 및 냉각과정을 거치면서 오염도가 다시 증가하여 이 과정에서 냉각수 및 성형떡의 고물관리에 대한 주의를 시사하였다. 떡의 제조환경에 대한 미생물학적 오염도 분석결과, 쌀 분쇄기 및 떡고물 작업환경에 대한 오염 수준이 높게 나타났으며, 성형기에서도 일반세균, 대장균 및 B. cereus가 검출되어 작업환경에서의 기구 및 제조설비 관리가 필요하였다. 제조설비 및 환경에서의 오염은 원재료와의 교차오염을 일으킬 수 있으므로 체계적인 세척 및 소독 등으로 미생물학적 위해를 감소시켜야 할 것으로 사료된다. The purpose of this study was to evaluate the microbial contamination level of Korean traditional rice cakes (Garaetteok, Injeolmi, Gyeongdan), as well as manufacturing environment of small-sized businesses in Korea. The contamination levels of total aerobic bacteria, coliforms, and Bacillus cereus in raw materials were 3.76-4.48, 2.21-4.14, and 1.02-1.15 log CFU/g respectively. On the other hand, Escherichia coli was not found. It has been found that the contamination level of total aerobic bacteria, coliforms, and B. cereus in the raw material decreased after the washing process, but it increased again during the soaking and grinding process. However, after the steaming stage, the contamination level increased again during the molding and cooling process, suggesting the need to take cautions in managing cooling water and molded rice cakes in the process. These results suggest that the safe management of cooling water and taking cautions in the drying process after steaming of rice cakes are necessary for controlling cross-contamination. No E. coli was detected during the manufacturing process involving all tested rice cakes. The microbial contamination level of manufacturing environment such as rice grinder and rice cake forming machine was high. Therefore, in terms of food safety strategy, it is necessary to consider introducing systematic cleansing and disinfection procedure to processing equipment and environment for the sake of reducing microbiological risks.

시루떡의 제조공정 중 미생물 저감화 연구

한상하,김경준,박준하,변계환,최송이,하상도 한국식품저장유통학회 2022 한국식품저장유통학회지 Vol.29 No.5

This study was conducted to establish effective reduction strategy during the manufacturing process of rice cakes. Simple washing (3 times) and ultrasonic washing (40 kHz, 10 min) were used in the rice washing process, and sodium hypochlorite (100 ppm, 5 min) and chlorine dioxide (20 ppm, 5 min) were used as chemical disinfectants. Combination treatment using ultrasonic washing and the two chemical disinfectants was also performed. The chemical disinfectants were more effective than the ultrasonic cleaning in a single treatment of each method, and sodium hypochlorite showed a greater reduction effect than chlorine dioxide. The combination treatment using both chemical disinfectant and ultrasonic cleaning was found to be more effective than using a single treatment, and no significant difference was observed in the results based on the disinfectant used. During the heating process, which is an important control point of HACCP system, total aerobic bacteria, coliforms, Bacillus cereus and Escherichia coli were inactivated. UV sterilization (30 min, 60 min) was applied as the nonthermal treatment and compared with the general drying method (5, 12 h) during the cooling process of rice cakes. No bacteria were not found after the treatment, whereas the total number of bacteria in the naturally dried rice cakes increased after 12 h, indicating the potential of UV sterilization as an important control point during the cooling process of rice cakes.

떡류 경영업체의 미생물학적 위생관리 전략

한상하,박준하,박상혁,허은,변계환,최송이,하상도 한국식품과학회 2022 식품과학과 산업 Vol.55 No.4

Rice cakes are a traditional Korean food made with rice flour as the main ingredient. The consumption of rice cakes has been steadily increasing until recently, and the market for rice cake consumption is also growing. However, rice cakes have a lot of moisture and high water activity, so they are suitable for microbial growth. In addition, since most of the companies that manufacture rice cakes are small businesses, research on microbial contamination reduction measures suitable for these environments is needed. Therefore, this paper investigated the overall status of the domestic rice cake industry and recent trends were analyzed, and the safety standards of current rice cakes were investigated. In addition, studies on reducing pathogenic bacteria on rice cakes by physical and chemical methods that can be used in smallscale manufacturing processes were further reviewed

Quantitative microbial risk assessment for Clostridium perfringens foodborne illness following consumption of kimchi in South Korea

최유경,강주현,이예원,서영은,이희영,김세정,이지연,하지명,오혜민,김유진,변계환,하상도,윤요한 한국식품과학회 2020 Food Science and Biotechnology Vol.29 No.8

The purpose of this study was to conduct a riskassessment for Clostridium perfringens foodborne illnessvia kimchi consumption in South Korea. Prevalence of C. perfringens in kimchi, kimchi consumption amount andfrequency, and distribution conditions (time and temperature)from manufacture to the home were determined. C. perfringens initial contamination level was estimated usingBeta distribution [Beta (6, 79)]. Potential C. perfringenscell counts during distribution were predicted using theWeibull model (primary models, R2=0.923–0.953) and apolynomial model [(δ=1/(0.2385+(−0.03079Temp)+(0.00119Temp2)), R2=0.719]. Average daily consumptiondata was assessed using Gamma distribution [1.0444,91.767, RiskShift (0.16895), RiskTruncate (0, 1078)]. Themean risk of C. perfringens-associated foodborne illnessfollowing kimchi consumption was found to be 1.21910−17. These results suggest that the risk of C. perfringensfoodborne illness from kimchi consumption, under currentconditions, can be considered to be very low in S. Korea.