• Journal of Food Hygiene and Safety
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• v.33 no.1
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• pp.65-70
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• 2018

Monitoring of Listeria monocytogenes, the causative agent of listeriosis, in food is inportant for public health. The Korean Food Standards Codex has adopted a 'zero-tolerance' policy for L. monocytogenes. The standard detection method of L. monocytogenes is based on enrichment. Thus, proper enrichment methods need to be instituted to ensure quality control of the detection procedures. In this study, the growth of L. monocytogenes and Listeria innocua as a mixed culture in Listeria enrichment broth (LEB) was monitored during artificial contamination of enrichment culture. We confirmed competitive growth or interspecies inhibitory activity of L. monocytogenes and L. innocua. Interspecies growth differences and the inhibitory activity of different inoculation and mixtures L. innocua against L. monocytogenes were examined. The concentration of L. monocytogenes must be 2.0 log CFU/mL or more than L. innocua to grow better than L. innocua. It is known that Listeria spp. and L. monocytogenes show growth difference during LEB, resulting in the risk of false-negative results. The inhibition of L. monocytogenes by L. innocua was always observed when present at lower concentrations. However, it was confirmed that L. innocua suppressed when L. monocytogenes was present at a higher concentration. Therefore if a mixture of Listeria spp. is present, detecting L. monocytogenes is difficult. Thus, a new enrichment broth to improve the detection rate of L. monocytogenes is needed.

• Korean Journal of Veterinary Research
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• v.43 no.2
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• pp.231-237
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• 2003

Listeria (L.) monocytogenes in samples could not be detected occasioally by faster growth of other Listeria spp. especially L. innocua. The aim of this study was to develop the differential media and multiplex polymerase chain reaction (PCR) assays for the rapid detection of L. monocytogenes. L. monocytogenes colonies were characterized by their ${\beta}$-hemolysis with fluorescence under 366 nm UV light on the Listeria hemolysis agar (LHA). L. innocua, a species commonly present in foods, did not produce ${\beta}$-hemolysis on LHA. Therefore, one or more colonies of L. monocytogenes were easily distinguished from large populations of L. innocua. The multiplex PCR assays were developed to distinguish from L. monocytogenes and other Listeria spp. with two pairs of primers. The primers were designed in 16S rRNA and listeriolysin O gene for specific amplification of all members of the genus Listeria and L. monocytogenes, respectively. The multiplex PCR assays produced 560 and 938 bp products in L. monocytogenes; only 938 bp products in the genus Listeria. The multiplex PCR assays could detect as little as 50 pg of L monocytogenes DNA. These results indicated that the differential media and multiplex PCR assays might be useful diagnostic tools for the rapid detection of L. monocytogenes.

• Journal of the Korean Society of Food Science and Nutrition
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• v.23 no.2
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• pp.293-297
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• 1994

The effect of organic acids on growth and heat resistance of Listeria monocytogenes Scott A were investigated. The growth of L. monocytogenes was inhibited in Tryptic Soy Broth(TSB) with 0.1 or 0.2% of acetic , tartic , propionic , citric and lactic acid at 35$^{\circ}C$, respectively. The growth of l. Monocytogenes did not occur in TSB with 0.2% of acetic acid or propionic acid during 48h of incubation. The heat resistance of L.monocytogenes was affected by kind of organic acid, ph and heating substrate. L.monocytogenes showed more heat resistant in TSB with various organic acids than in 0.1M sodium phosphate with the same organic acids. Heat resistance decreased as pH of heating substrate decreased . Surface-adherent microcolony was more heat resistant than planktonic cell of L. monocytogenes. Propionic and lactic acids more affected on heat resistance of L.monocytogenes than acetic , tartaric and citric acids.

• Korean Journal of Food Science and Technology
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• v.26 no.5
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• pp.545-551
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• 1994

Ethanol extract of barks, roots, stems, leaves and seeds of 49 species of plants were examined their growth inhibition by disk method on Listeria monocytogenes ATCC 19111, ATCC 19112, ATCC 19113, ATCC 19114 and ATCC 15313. The extracts exhibited comparatively strong growth inhibition were compared their activity with broth culture containing different concentration of the extracts. L. monocytogenes ATCC 19111 was inhibited by Siegesbeckia pubescens Makino and Morus alba Linne (Ma) extracts. L. monocytogenes ATCC 19112 and ATCC 19114 were inhibited by Ma extract. ATCC 19113 was inhibited by Sophora flavescens AITON and Ma extract. ATCC 15313 was inhibited by Foeniculum vulgare Gaertner, Prunella vulgaris Var lilacina Nakai and Ma extract. Ma extract showed comparatively good inhibition effect for 5 strains of L. monoytogenes. 500 ppm of Ma extract almost inhibited the growth of all L. monocytogenes tested.

• Korean Journal of Food Science and Technology
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• v.31 no.5
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• pp.1324-1329
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• 1999

This study was carried out to investigate the distribution and characteristics of Listeria monocytogenes isolated from frozen Mandoo and pizza in 1998. A total 72 samples were examined and USDA, FDA and modified cold enrichment methods were used for the detection of Listeria spp. Overall prevalence of L. monocytogenes in frozen foods was 9.7% and L. monocytogenes was isolated from 11.1% of frozen Mandoo and 5.6% of frozen pizza. The highest detection rate of Listeria spp. in frozen Mandoo was found at USDA method and the serotype of L. monocytogenes isolates was 4. Isolated L. monocytogenes was confirmed by PCR method with Hly 1 and 2 as primers. It would be necessary to develop more rapid and specific method to isolate and confirm L. monocytogenes from foods because USDA and PCR methods used in this study took 3-4 days. D value of L. monocytogenes isolate in tryptic soy broth was 49.2 sec at $60^{\circ}C$ and 8.8 sec $at\;65^{\circ}C$, and D value of L. monocytogenes in foods with high distribution rate of Listeria spp. would be necessary to evaluate for the safe use of frozen foods.

• Microbiology and Biotechnology Letters
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• v.25 no.5
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• pp.442-447
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• 1997

To development food preservative, antimicrobial activities of Schizandra chinensis (SC) against Listeria monocytogenes Scott A, L. monocytogenes Brie I and L. monocytogenes ATCC 19111 were investigated. The growth of L. monocytogenes Scott A, L. monocytogenes Brie I and L. monocytogenes ATCC 19111 was inhibited apparently in Tryptic Soy Broth (TSB) containing 1% SC at 35$\circ$C and it was found that these had antibacterial effects against a broad spectrum of pathogenic bacteria such as S. aureus ATCC 29737, B. subtilis KCTC 1021, E. coli ATCC 11775. The growth of L. monocytogenes was also inhibited about 3 to 5 log$_{10}$ cycle by 0.1% of three fractions of the alcohol extract such as ether, ethyl acetate and butanol. Acidic, weakly acid and neutral fraction of ether fraction showed inhibitory properties against L. monocytogenes.

• Food Science of Animal Resources
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• v.33 no.4
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• pp.481-486
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• 2013

This study evaluates the effects of fat contents on the thermal resistance, antibiotic sensitivity, and Caco-2 cell invasion of Listeria monocytogenes. Ten strain mixture of L. monocytogenes in milk (0, 1, and 4% fat) and pork sausage patties (10, 20, and 30% fat) were exposed to $63^{\circ}C$. To evaluate effects of fat on the antibiotic sensitivity of L. monocytogenes, the L. monocytogenes strains NCCP10811 (most antibiotic resistant to streptomycin) and NCCP10943 (most antibiotic sensitive to streptomycin) were exposed to different fat contents in milk and pork sausage patties, and L. monocytogenes from the foods were used for antibiotic sensitivity assays. The most invasive L. monocytogenes strains (NCCP10943) was exposed to different fat contents in milk or pork sausage patties, and L. monocytogenes from the foods were used for the Caco-2 cell invasion assays. The reductions of L. monocytogenes populations were not generally influenced by fat contents. The L. monocytogenes subjected to milk fat had increased sensitivities (p<0.05) due to some antibiotics. In addition, Caco-2 cell invasion efficiency of L. monocytogenes NCCP10943 increased (p<0.05) as fat contents increased. These results indicated that higher fat contents may be related to L. monocytogenes invasions and heat resistances in pork sausage patties, but the relationship between fat and antibiotic sensitivity varied according to antibiotics, strains, and fat contents.

• Food Science of Animal Resources
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• v.33 no.3
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• pp.395-402
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• 2013

Sodium chloride is used to improve various properties of processed meat products, e.g., taste, preservation, water binding capacity, texture, meat batter viscosity, safety, and flavor; however, many studies have shown that sodium chloride increases the resistance of many foodborne pathogens to heat and acid. Listeria monocytogenes has been isolated from various readyto- eat (RTE) meat and dairy products formulated with sodium chloride; therefore, the objective of this paper was to review the effects of sodium chloride on the physiological characteristics of L. monocytogenes. The exposure of L. monocytogenes to sodium chloride may increase biofilm formation on foods or food contact surfaces, virulence gene transcription, invasion of Caco-2 cells, and bacteriocin production, depending on L. monocytogenes strain and serotype as well as sodium chloride concentration. When L. monocytogenes cells were exposed to sodium chloride, their resistance to UV-C irradiation and freezing temperatures increased, but sodium chloride had no effect on their resistance to gamma irradiation. The morphological properties of L. monocytogenes, especially cell elongation and filament formation, also change in response to sodium chloride. These findings indicate that sodium chloride affects various physiological responses of L. monocytogenes and thus, the effect of sodium chloride on L. monocytogenes in RTE meat and dairy products needs to be considered with respect to food safety. Moreover, further studies of microbial risk assessment should be conducted to suggest an appropriate sodium chloride concentration in animal origin foods.

• Korean Journal of Veterinary Research
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• v.36 no.1
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• pp.119-129
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• 1996

The present study was conducted to rapidly detect Listeria monocytogenes in raw milk. Specificity and sensitivity of polymerase chain reaction(PCR) technique, and direct PCR were examinded in raw milk, also were compared the calssical culture methods with PCR technique. This method used a pair of primers based on a unique region in the 16S rRNA sequence of L nomocytogenes. In the PCR specificity tests, each of the 10 strains of L monocytogenes tested gave a single 70-bp band. But the other six Listera spp tested gave negative results. Results of the sensitivity tests showed that as few as 2 CFU of L monocytogenes in pure cultures could be detected with 16S rRNA-based primers, L-1 and L-2. In different PCR cycles, a PCR product was detected with $10^3$ cells of L monocytogenes from 25 cycles to 50 cycles and the concentration of PCR products was cycle-dependent. Raw milk samopes added L monocytogenes cells gave negative results. However, these samplers gave a single 70-bp band by pretreatment of pronase, and PCR products were detected with $10^1$ cells of L monocytogenes. To detemine the most sensitive culture protocol to use in conjunction with the PCR assay, raw milk samples were inoculated with L monocytogenes at concentrations ranging from 1 to $5.7{\times}10^4CFU/ml$. PCR assays from Listeria enrichment broth(LEB) containing raw milk samples added L monocytogene EGD could dtect 10 cells in pronase-pretreated samples without incubation, and 1 cell of L monocytogenes in both 12 hr and 24 hr incubation, respectively. Isolation raw of PCR assays was similar to that of classical culture methods, but required time for detection of L monocytogenes could remarkably be reduced compare to culture methods.

• Journal of Microbiology and Biotechnology
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• v.19 no.3
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• pp.238-249
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• 2009

The genus Listeria consists of six closely related species and forms three phylogenetic groups: L. monocytogenes-L. innocua, L. ivanovii-L. seeligeri-L. welshimeri, and L. grayi. In this report, we attempted to examine the evolutionary relationship in the L. monocytogenes-L. innocua group by probing the nucleotide sequences of 23S rRNA and 16S rRNA, and the gene clusters lmo0029-lmo0042, ascB-dapE, rplS-infC, and prs-ldh in L. monocytogenes serovars 1/2a, 4a, and 4b, and L. innocua. Additionally, we assessed the status of L. monocytogenes-specific inlA and inlB genes and 10 L. innocua-specific genes in these species/serovars, together with phenotypic characterization by using in vivo and in vitro procedures. The results indicate that L. monocytogenes serovar 4a strains are genetically similar to L. innocua in the lmo0035-lmo0042, ascB-dapE, and rplS-infC regions and also possess L. innocua-specific genes lin0372 and lin1073. Furthermore, both L. monocytogenes serovar 4a and L. innocua exhibit impaired intercellular spread ability and negligible pathogenicity in mouse model. On the other hand, despite resembling L. monocytogenes serovars 1/2a and 4b in having a nearly identical virulence gene cluster, and inlA and inlB genes, these serovar 4a strains differ from serovars 1/2a and 4b by harboring notably altered actA and plcB genes, displaying strong phospholipase activity and subdued in vivo and in vitro virulence. Thus, by possessing many genes common to L. monocytogenes serovars 1/2a and 4b, and sharing many similar gene deletions with L. innocua, L. monocytogenes serovar 4a represents a possible evolutionary intermediate between L. monocytogenes serovars 1/2a and 4b and L. innocua.