This study investigated the physical properties of polymers and antimicrobial activities of organic acids on Listeria monocytogenes to develop hydrogels. κ-carrageenan (1, 2, and 3%), carboxymethylcellulose (CMC; 1, 3, and 5%), and agar (1.5 and 3%) were mixed with cross-linkers (Na+, K+, Ca2+, and Al3+) or each other by stirring or heating to form cross-linkage, and their physical properties (hardness, elasticity, and swelling) were measured. The hydrogels formulated with organic acid (1, 3, and 5%) were analyzed by spot assay against L. monocytogenes. κ-carrageenan formed hydrogels with high hardness without other cross-linkers, but they had low elasticity. The elasticity was improved by mixing with other cross-linkers such as K+ or other polymer, especially in 3% κ-carrageenan. CMC hydrogel was formed by adding cross-linkers Al3+, Na+, or Ca2+, especially in 5% CMC. Thus, stickiness and swelling for selected hydrogel formulations (two of κ-carrageenan hydrogels and three of CMC hydrogels) were measured. Among the selected hydrogels, most of them showed appropriate hardness, but only 3% κ-carrageenan-contained hydrogels maintained their shapes from swelling. Hence, 3% κ-carrageenan+0.2% KCl and 3% κ-carrageenan+1% alginate+0.2% KCl+0.2% CaCl2 were selected to be formulated with lactic acid, and showed antilisterial activity. These results indicate that 3% κ-carrageenan hydrogels formulated with lactic acid can be used to control L. monocytogenes on food surface.

The objective of this study is to assess immunomodulatory effects of mixed Weissella (W.) cibaria JW15 strain with water extract of black soybean (Glycine max) and burdock (Arctium lappa) on Listeria (L.) monocytogenes infection in mice. Female 7-9 week old BALB/c mice were given a daily dose of 1 × 109 CFU of viable JW15 and JW15 mixed with black soybean (BS) and burdock (BD) in 200 μL PBS for 2 weeks. The nomal control group (NC) and positive control group (PC) were given 200 μL PBS. After 2 weeks, mice were infected with L. monocytogenes (1.0 × 105 CFU/mouse) via the tail vein. The NC was injected with 100 μL PBS without L. monocytogenes. After 2 days, mice were euthanized and their body weights were determined. In addition, their livers and spleens were weighed, and serum were analyzed for cytokine (Interleukin-1β (IL-1β) and Tumor necrosis factor-α (TNF-α)) production. The survival rate was monitored using 5 mice in each group in the same way above until the mice died. Two days after infection with L. monocytogenes, mean spleen weight per body weight (g/kg) of JW15 (5.4 ± 0.88 g/kg), JW15 + BS (6.0 ± 0.64 g/kg), and JW15 + BD (5.3 ± 0.38 g/kg) group were significantly lower than that of the PC (6.8 ± 0.57 g/kg). The level of IL-1β in the serum of JW15 + BD (113.6 ± 31.03 pg/mL) was significantly higher than that of the JW15 (67.9 ± 15.15 pg/mL). Collectively, combination W. cibaria JW15 and water extract of BD and BD have ability to induce synergistic immunomodulative effects and are suitable for consideration as a functional food for humans and functional feed additives for companion animals.

This study was conducted to investigate the effect of cold plasma combined with UV-C irradiation against Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes on lettuce. E. coli O157:H7, S. Typhimurium, and L. monocytogenes, corresponding to approximately 5.82, 5.09, 5.65 log CFU/ g, were inoculated on lettuce, respectively. Then, the lettuce was treated with cold plasma, UV-C and combination (cold plasma + UV-C), respectively. The treated lettuce was stored for 9 days at 4oC for microbiological analysis and sensory evaluation. Cold plasma reduced the populations of E. coli O157:H7, S. Typhimurium, and L. monocytogenes by 0.26, 0.65, and 0.93 log CFU/g, respectively. Each microorganism were reduced by 0.87, 0.88, and 1.14 log CFU/ g after UV-C treatment. And, the combined treatment that was treated by cold plasma after UV-C treatment reduced the populations of inoculated microorganisms by 1.44, 2.70, 1.62 log CFU/g, respectively. The all treatment significantly (p < 0.05) reduced the populations of all inoculated bacteria compared to untreated lettuce. UV-C combined with cold plasma was the most effective for reducing the pathogenic bacteria on lettuce, by showing log-reductions of ≥ 2.0 log CFU/g. All treatment was not significantly different until 6 day storage compared to control group in terms of appearance, texture and overall acceptability. Therefore, the combined treatment will be an effective intervention method to control the bacteria on lettuce.

본 연구는 다양한 냉동과 해동처리에 따른 계육 가슴살에 natural microflora, 접종된 L. monocytogenes와 C. jejuni 수와 미세구조 변화 구명을 위하여 연구를 수행하였다. −20℃ 송풍식 냉동처리구의 총 호기성 세균과 C. jejuni 수는 4.06 log CFU/g과 4.09 log CFU/g으로 대조구와 비교하여 각각 약 0.7 log CFU/g과 1.0 log CFU/g의 감소를 보였다. 한편, 계육 가슴살 접종된 L. monocytogenes 수는냉동방법과 냉동온도에 따라 유의적인 차이를 보이지 않았다. 4℃와 25℃ 송풍식 해동처리구의 총 호기성 세균수는 3.70 log CFU/g과 4.02 log CFU/g으로 측정되어 대조구와 비교하여 각각 0.72 log CFU/g과 0.40 log CFU/g 감소한 반면 25℃ 유수식 해동처리구의 총 호기성 세균 수는 해동과정에서 균수가 급격히 증가하여 5.78 log CFU/g으로 관찰되었다. 해동 중 C. jejuni 수 변화는 해동방법보다 해동온도에 영향을 받는 것으로 나타났다. 냉동-해동반복 5회 후 총 호기성 세균과 효모 및 곰팡이 수는 감소하여 각각 4.15 log CFU/g과 2.30 log CFU/g을 보였다. 계육 가슴살에 접종된 L. monocytogenes 수는 냉동-해동 반복처리에 유의적인 영향이 없었지만 C. jejuni 수는 냉동-해동 반복 횟수가 증가함에 따라 감소하는 경향을 보였다. 냉동-해동 반복이 증가함에 따라 근섬유 조직을 재 손상시켰으며 특히 냉동-해동 반복 5회 후에는 계육 가슴살 시료의 조직세포 외부뿐만 아니라 내부에서도 공간이 발생하였으며 불균일하게 찢어진 세포가 관찰되었다.

본 연구에서는 김치로부터 W. cibaria 0D17와 W. confuse 0D23를 생화학적 특성 분석과 16s rRNA 염기서열 분석을 통해 분리, 동정하였으며, W. cibaria 0D17와 W. confuse 0D23 배양 상등액이 L. monocytogenes에 대한 항균 효과가 있는 것으로 나타났다. 또한, 실시간 정량 PCR을 통해 W. cibaria 0D17 및 W. confusa 0D23가 L. monocytogenes 를 공동 배양했을 때의 생육억제 효과를 분석한 결과, 37℃에서는 생육 억제 효과가 있는 것으로 확인되었다. 따라서, 김치 유래 Weissella spp. 가 갖는 L. monocytogenes에 대한 항균 활성에 대한 기초 자료로 활용가능 할 것으로 판단되며, W. cibaria 0D17 및 W. confusa 0D23가 생산하는 bacteriocin 등의 항균 물질 특성에 대한 연구가 추가 적으로 진행될 필요가 있을 것이다.

본 연구에서는 식품에서의 L. monocytogenes에 대한 기 초자료를 제공하고자 2010년부터 2011년까지 서울지역에서 수거된 식품 총 1042건에서 L. monocytogenes를 분리 하여 항생제 감수성 검사를 하였다. 김밥 4건(0.8%), 육회 4건(2.6%), 연어제품 2건(11.1%), 돈육식품과 조리된 생선에서 각 1건씩(각5.9%, 6.3%) 총 12균주가 분리 동정되었다. 분리 균주를 20종의 항생제에 검사한 결과 대다수 항생제(16종)에 감수성을 나타내었지만 cefotetan (11균주), cefotaxime (7균주), cefepime (6균주)에서 내성을 나타냈으며 3균주에서 임상치료에 자주 사용되는 tetracycline에 대해서 내성을 나타내었다.

Listeria monocytogenes continues to be a important food safety concern. The aims of the present study were to investigate the prevalence and antimicrobial susceptibility of L. monocytogenes. A total of 1,042 samples was collected from 2010 to 2011 in Seoul and twelve L. monocytogenes were isolated. Isolation rate was Gimbap (0.8%), Beef (yukhoe) (2.6%), Pork (cooked) (5.9%), Fish(cooked) (6.3%), and Salmon (11.1%), respectively. In this study, most of the isolates were susceptible to antibiotics. The most common resistance was cefotetan on 11 isolates, followed by cefotaxime on 7 isolates, cepefime on 6 isolates and tetracyclin on 3 isolates.

Peptidoglycan recognition proteins (PGRPs) are family of innate immune molecules that recognize bacterial peptidoglycan. PGRP-LE, a member of the PGRP family, selectively binds to diaminopimelic acid (DAP)-type peptidoglycan to activate both the immune deficiency (IMD) and proPhenoloxidase (proPO) pathways in insects. A PGRP-LE-dependent induction of autophagy to control Listeria monocytogenes has also been reported. We identified and partially characterized a novel PGRP-LE homologue, from Tenebrio molitor and analyzed its functional role in the survival of the insect against infection by a DAP-type PGN containing intracellular pathogen, L. monocytogenes. The cDNA is comprised of an open reading frame (ORF) of 990 bp and encodes a polypeptide of 329 residues. TmPGRP-LE contains one PGRP domain, but lacks critical residues for amidase activity. Quantitative RT-PCR analysis showed a broad constitutive expression of the transcript at various stages of development spanning from larva to adult. RNAi mediated knockdown of the transcripts followed by a challenge with L. monocytogenes showed a significant reduction in survival rate of the larvae, suggesting a putative role of TmPGRP-LE in sensing and control of L. monocytogenes infections in T. molitor. These results implicate PGRP-LE as a defense protein necessary for survival of T. molitor against infection by L. monocytogenes.

Apolipophorin III (apoLp-III) is a well-known hemolymph protein having a functional role in lipid transport and immune response of insects. We cloned full-length cDNA encoding putative apoLp-III from larvae of the coleopteran beetle, Tenebrio molitor (TmapoLp-III), by identification of clones corresponding to the partial sequence of TmapoLp-III, subsequently followed with full length sequencing by a clone-by-clone primer walking method. The complete cDNA consists of 890 nucleotides, including an ORF encoding 196 amino acid residues. Excluding a putative signal peptide of the first 20 amino acid residues, the 176-residue mature apoLp-III has a calculated molecular mass of 19,146 Da. Genomic sequence analysis with respect to its cDNA showed that TmapoLp-III was organized into four exons interrupted by three introns. Several immune-related transcription factor binding sites were discovered in the putative 5’-flanking region. BLAST and phylogenetic analysis reveals that TmapoLp-III has high sequence identity (88%) with Tribolium castaneum apoLp-III but shares little sequence homologies (<26%) with other apoLp-IIIs. Homology modeling of Tm apoLp-III shows a bundle of five amphipathic helices, including a short helix 3’. The ‘helix-short helix-helix’ motif was predicted to be implicated in lipid binding interactions, through reversible conformational changes and accommodating the hydrophobic residues to the exterior for stability. Highest level of TmapoLp-III mRNA was detected at late pupal stages, albeit it is expressed in the larval and adult stages at lower levels. The tissue specific expression of the transcripts showed significantly higher numbers in larval fat body and adult integument. In addition, TmapoLp-III mRNA was found to be highly up-regulated in late stages of L. monocytogenes or E. coli challenge. These results indicate that TmapoLp-III may play an important role in innate immune responses against bacterial pathogens in T. molitor.

In this study, the transfer rate of wild type Listeria monocytogenes (LM) was investigated to establish the standard of safety management during pork meat processing for meat to meat and meat to food contact surfaces contamination at 5 and 10oC. The transfer rate of LM from meat to meat during the processing increased from 0.02% after 30 min to 0.42% after 120 min at 5oC, while for conveyor belt and stainless steel, it decreased from 0.015% and 0.013% after 30 min to 0.002% and 0.0003% after 120 min at 5oC, respectively (p < 0.05). When temperature increased to 10oC, the transfer rates of LM from meat to meat, conveyor belt and stainless steel were the highest at 60 min exposure, and all decreased after 120 min. In reverse, the transfer rate from food contact surface to pork meat was significantly higher than that from pork meat to food contact surface (p < 0.01). Also, the transfer rate to conveyor belt was significantly higher than stainless steel (p < 0.05) and it was highest at 30 min exposure time in both 5 and 10oC. This study indicates that the transfer and adherence rates of LM are influenced by the contact time and temperature. Consequently, these results were utilized to develop a predictive model with a high level of confidence which can lead to prevent cross-contamination during pork meat processing.

This study was performed to determine the transfer rates of each foodborne pathogen from pork meat packaging during the processing. We analyzed the transfer rate of Listeria monocytogenes from contaminated pork meat to worker's hands (wearing polyethylene gloves, PEG; cotton gloves, CG; and bare hands), cutting boards and knives, and vice versa. Transfer rate of CG 100.00% was higher than that of bare hands 2.513% and PEG 1.511%. In particular, when wearing CG, the transfer rate from the CG to bare hands with CG was 0.08%. Also, the range of transfer rates from contaminated pork meat to cutting board and knife was 0.352-3.791%. In contrast, transfer rates from the workers’ hands (with PEG/CG and bare hands) to cutting board, knife, and pork meat ranged from 0.001 to 0.141%. There was a lower transfer rate from workers’ hands than from pork meat. These findings indicate that use of PEG could effectively reduce or prevent the cross-contamination compared to CG and provide important information concerning the consecutive transfer of L. monocytogenes during food processing.

We investigated the prevalence of the Listeria monocytogenes from livestock processed products in processing plants and retail markets of Korea from 2010 to 2011. A total of 1,380 samples were collected; Meat processed products such as cooked ham and sausage, jerked meat, and meat extract products. Milk processed products such as milk, butter, cheese, and ice cream. Egg processed products such as whole egg liquid and pidan. L. monocytogenes were isolated from samples using listeria enrichment broth, fraser broth and Oxford agar, and counted in Oxford agar. The three of L. monocytogenes strains (1.16%) were isolated from sausages, two (0.73%) from mixed pressed ham and one (0.51%) from jerked meat, respectively. The colony forming unit (CFU) of L. monocytogenes from all samples were below 10 CFU/g. The four isolates (66.6%) were 1/2b except two isolates (1/2a) in the serotypes. Further studies are needed to understand the transmission route of L. monocytogenes, including a survey of food handlers, environments of retail markets, and all potential risk factors in cooked sausages, mixed pressed hams, and jerked meat processing.

Predictive mathematical models were developed for predicting the kinetics of growth of Listeria monocytogenes in smoked salmon, which is the popular ready-to-eat foods in the world, as a function of temperature (4, 10, 20 and 30℃). At these storage temperature, the primary growth curve fit well (r² = 0.989~0.996) to a Gompertz equation to obtain specific growth rate (SGR) and lag time (LT). The Polynomial model for natural logarithm transformation of the SGR and LT as a function of temperature was obtained by nonlinear regression (Prism, version 4.0,GraphPad Software). Results indicate L. monocytogenes growth was affected by temperature mainly, and SGR model equation is 365.3-31.94*Temperature+0.6661*Temperature^2 and LT model equation is 0.1162-0.01674*Temperature+0.0009303*Temperature^2. As storage temperature decreased 30℃ to 4℃, SGR decreased and LT increased respectively. Polynomial model was identified as appropriate secondary model for SGR and LT on the basis of most statistical indices such as bias factor (1.01 by SGR, 1.55 by LT) and accuracy factor (1.03 by SGR, 1.58 by LT).

In this study, two duplex real-time PCR approach with melting curve analysis is presented for the detection of Escherichia coli O157:H7, Listeria monocytogenes, Salmonella spp. and Staphylococcus aureus, which are important food-borne bacterial pathogens usually present in fresh and/or minimally processed vegetables. Reaction conditions were adjusted for the simultaneous amplification and detection of specific fragments in the β-glucuronidase (uidA, E. coli), thermonuclease (nuc, S. aureus), hemolycin (hly, L. monocytogenes) and tetrathionate reductase (ttr, Salmonella spp.) genes. Melting curve analysis using a SYBR Green I real-time PCR approach showed characteristic Tm values demonstrating the specific and efficient amplification of the four pathogens; 80.6 ± 0.9 ℃,86.9 ± 0.5 ℃, 80.4 ± 0.6 ℃ and 88.1 ± 0.11 ℃ for S. aureus, E. coli O157:H7, L. monocytogenes and Salmonella spp.,respectively. For all the pathogens, the two duplex, real-time PCR was equally sensitive to uniplex real-time PCR,using same amounts of purified DNA, and allowed detection of 10 genome equivalents. When our established duplex real-time PCR assay was applied to artificially inoculated fresh lettuce, the detection limit was 10³ CFU/g for each of these pathogens without enrichment. The results from this study showed that the developed duplex real-time PCR with melting curve analysis is promising as a rapid and cost-effective test method for improving food safety.

In this study, predictive mathematical models were developed to predict the kinetics of Listeria monocytogenes growth in the mixed fresh-cut vegetables, which is the most popular ready-to-eat food in the world, as a function of temperature (4, 10, 20 and 30oC). At the specified storage temperatures, the primary growth curve fit well (r2 = 0.916~0.981) with a Gompertz and Baranyi equation to determine the specific growth rate (SGR). The Polynomial model for natural logarithm transformation of the SGR as a function of temperature was obtained by nonlinear regression (Prism, version 4.0, GraphPad Software). As the storage temperature decreased from 30oC to 4oC, the SGR decreased, respectively. Polynomial model was identified as appropriate secondary model for SGR on the basis of most statistical indices such as mean square error (MSE = 0.002718 by Gompertz, 0.055186 by Baranyi), bias factor (Bf = 1.050084 by Gompertz, 1.931472 by Baranyi) and accuracy factor (Af = 1.160767 by Gompertz, 2.137181 by Baranyi). Results indicate L. monocytogenes growth was affected by temperature mainly, and equation was developed by Gompertz model (−0.1606 + 0.0574*Temp + 0.0009*Temp*Temp) was more effective than equation was developed by Baranyi model (0.3502 − 0.0496*Temp + 0.0022*Temp* Temp) for specific growth rate prediction of L. monocytogenes in the mixed fresh-cut vegetables.

We constructed a standard curve to quantify Listeria monocytogenes in ready-to-eat product, especially sausage samples, using real-time PCR. A standard curve was generated using serially diluted L. monocytogenes cells in distilled water. When cells were artificially inoculated in 10 g of sausage samples in 90㎖ buffered peptone water, the cell concentration of range was approximately 1.0×108 to 100 CFU/㎖. The standard curve of the serially diluted cells was linear for at least seven orders of magnitude from 103 to 109 CFU/㎖ of L. monocytogenes. When cells were diluted in sausages, the linearity range was from 104 to 108 CFU/㎖. The correlation coefficient (R2) of diluted cells was 0.9888 and the slope of the curve was —2.6621. The coefficient and slope of inoculated samples were 0.9916 and —2.747, respectively. The R2 value for serially diluted L. monocytogenes and artificially contaminated sausage samples were acceptable. The approach described in this study represents the potency of the quantification of L. monocytogenes in sausage samples by quantitative real-time PCR. It can be used in monitoring the presence and persistence of this pathogen in sausages.