• Applied Biological Chemistry
• /
• v.42 no.1
• /
• pp.63-67
• /
• 1999

Growth rate and osmolyte accumulation of L. monocytogenes were measured at the varying concentrations of NaCl. L. monocytogenes accumulated glycine betaine and glutamate intracellularly when grown under osmotic stress by NaCl, and the amounts of them increased as the concentration of NaCl was increased. They were 685 and 345 nmol/mg protein, respectively, when grown in the BHI supplemented with 4% NaCl. In order to inhibit L. monocytogenes effectively, both NaCl and Morus alba L. leaf extract were supplemented in TSB, and antibacterial effect of those supplements on L. monocytogenes was tested. Growth of L. monocytogenes grown in TSB supplemented with 2% NaCl and 100 ppm M. alba leaf extract decreased by 10 times in CFU/ml unit comparing to the growth of control. When grown in TSB, supplemented with 2% NaCl plus 500 ppm M. alba leaf extract and 2% NaCl plus 1,000 ppm M. alba leaf extract, growth of L. monocytogenes decreased by $10^5\;and\;10^8$ times in CFU/ml unit, respectively.

• Food Science of Animal Resources
• /
• v.37 no.2
• /
• pp.320-328
• /
• 2017

In this study, two Listeria bacteriophages, LMP1 and LMP7, were isolated from chicken feces as a means of biocontrol of L. monocytogenes. Both bacteriophages had a lytic effect on L. monocytogenes ATCC 7644, 15313, 19114, and 19115. Phages LMP1 and LMP7 were able to inhibit the growth of L. monocytogenes ATCC 7644 and 19114 in tryptic soy broth at $10^{\circ}C$ and $30^{\circ}C$. Nevertheless, LMP1 was more effective than LMP7 at inhibiting L. monocytogenes ATCC 19114. On the contrary, LMP7 was more effective than LMP1 at inhibiting L. monocytogenes ATCC 7644. The morphology of LMP1 and LMP7 resembled that of members of the Siphoviridae family. The growth of L. monocytogenes ATCC 7644 was inhibited by both LMP1 and LMP7 in milk; however, the growth of L. monocytogenes ATCC 19114 was only inhibited by LMP1 at $30^{\circ}C$. The lytic activity of bacteriophages was also evaluated at $4^{\circ}C$ in milk in order to investigate the potential use of these phages in refrigerated products. In conclusion, these two bacteriophages exhibit different host specificities and characteristics, suggesting that they can be used as a component of a phage cocktail to control L. monocytogenes in the food industry.

• Korean Journal of Food Science and Technology
• /
• v.26 no.5
• /
• pp.627-632
• /
• 1994

The growth inhibitions of each strain on tryptic soy broth containing various concentration of 75% ethanol extract of Sinomenium acutum(Thunb.) Rehd. et wils and Glycyrrhiza glabra L. var. glandulifera Regel were compared which were exhibited comparatively strong growth inhibition on Listeria monocytogenes ATCC 19111, 19112, 19113, 19114 and 15313 at previous screening test by disk method. The Sinomenium acutum(Thunb.) Rehd. et wils extract showed partly effect by its concentration in broth to L. monocytogenes ATCC 19111 and 19114. The Glycyrrhiza glabra L. var. glandulifera Regel extract inhibited the growth of all test strains and even 100 ppm of the extract in the broth inhibited the growth of all test strains of L. monocytogenes for 12 to 48 hours. The extract stopped the growth totally of all strains in 500 ppm addition level. L. monocytogenes ATCC 19113 was more sensitive than other strains.

• Journal of Dairy Science and Biotechnology
• /
• v.27 no.2
• /
• pp.43-48
• /
• 2009

Listeria monocytogenes is a major concern in food processing environments because it is ubiquitous and can easily contaminate food during processing. Contaminated food and the surfaces in food facilities can serve as reservoirs of L. monocytogenes, which can lead to the serious foodborne illness listeriosis in consumers. L. monocytogenes can adhere to materials commonly used in food processing equipment and form biofilms. In the biofilm mode, L. monocytogenes is significantly more resistant to disinfection or sanitizers than its planktonic counterparts. Many researchers have studied the effects of surface materials on bacterial adhesion and the formation of biofilms. Recent studies have focused on preventing the establishment of L. monocytogenes in niches in the food plant environments.

• Korean Journal of Food Science and Technology
• /
• v.36 no.3
• /
• pp.456-460
• /
• 2004

Effects of sigma factor (${\sigma}^{B}$) on biofilm formation in Listeria monocytogenes 10403S and ${\sigma}^{B}-deficient$ sigB null mutant were studied under high osmotic and low temperature conditions. In brain heart infusion (BHI) medium containing 6% NaCl, wild type 10403S and ${\sigma}^{B}-deficient$sigB null mutant formed biofilms of $6.83{\pm}0.38\;and\;5.33{\pm}0.45\;log\;cfu/cm^{2}$, respectively. L. monocytogenes 10403S in BHI medium containing 6% NaCl formed 4.7 times larger biofilm than without NaCl. Culture of L. monocytogenes 10403S and sigB null mutant at $4^{\circ}C$ did not show any significant differences in biofilm formation. The results suggest biofilm formation is activated by ${\sigma}^{B}$ and NaCl, whereas not affected by low temperature stress in L. monocytogenes 10403S. More studies are necessary to determine biofilm formation mechanism in osmotolerant L. monocytogenes.

• Food Science and Preservation
• /
• v.17 no.3
• /
• pp.425-429
• /
• 2010

Inactivation by UV-C irradiation of Listeria monocytogenes cocktail inoculated on hamburger patties was examined. Hamburger patty samples were inoculated with 6-7 log CFU/mL of L. monocytogenes cocktail, and then exposed to doses of 0, 1, 5, or $10kJ/m^2$ of UV-C light, followed by storage at $4{\pm}1^{\circ}C$ for 7 d. Microbiological evaluation indicated that the populations of L. monocytogenes decreased significantly (p<0.05) as irradiation dose increased. In particular, L. monocytogenes populations decreased by 2.03 log CFU/g after exposure to 10 $kJ/m^2$, compared with control samples. The thiobarbituric acid-reactive substance levels of hamburger patty samples increased during storage, regardless of UV-C irradiation status. These results indicate that UV-C irradiation may be useful in improving the microbial safety of hamburger patties during storage.

• Food Science of Animal Resources
• /
• v.30 no.5
• /
• pp.717-721
• /
• 2010

The objective of this study was to evaluate the inhibition of Listeria monocytogenes growth by oleanolic acid under sublethal stresses of NaCl and pH. L. monocytogenes ATCC15313 (6 log CFU/mL) was inoculated in microplate wells containing brain heart infusion (BHI) broth supplemented with oleanolic acid in various amounts (0, 0.25, 0.5, 1.0, 1.5, 2.0, and $4.0\;{\mu}g/mL$), and different pHs (5 and 7) and NaCl concentrations (0, 3, and 6%), followed by incubation under accelerated storage condition ($37^{\circ}C$, 48 h). The optical density (OD) of the samples was measured at 0, 6, 12, 24, and 48 h at 600 nm. After the lag phase duration was observed at the early stage of incubation, the OD values of L. monocytogenes significantly increased (p<0.05) in BHI broth formulated with 0 and 3% of NaCl during accelerated storage at pH 5 and 7. However, the growth of L. monocytogenes in 6% NaCl and at less than $0.5\;{\mu}g/mL$ of oleanolic acid had no growth at pH 5 and only gradual growth at pH 7. Moreover, L. monocytogenes generally had lower OD values as the concentrations of oleanolic acid increased. As expected, the OD values of L. monocytogenes were generally higher (p<0.05) at pH 7 than at pH 5. These results indicate that oleanolic acid should be useful in inhibiting the growth of L. monocytogenes.

• Journal of Microbiology and Biotechnology
• /
• v.14 no.3
• /
• pp.515-519
• /
• 2004

Listeria spp. were isolated from a total of 402 naturally contaminated domestic ready-to-eat (RTE) vegetable samples by the conventional Food and Drug Administration protocol and confinned by API-Listeria kit. Also, the susceptibility to 12 antibiotics, polymerase chain reaction (PCR) assay for virulence gene of pathogenic Listeria monocytogenes isolates, and in vitro virulence assay using myeloma and hybridoma cells from murine and human sources were tested. Among the samples, 17 samples (4.2％) were found to be contaminated with Listeria species. Among the 17 strains of Listeria spp. isolates, only 2 strains (11.8％) of L. monocytogenes and 15 strains (88.2％) of L. innocua were identified. Antibiotic susceptibility test showed that the Listeria spp. isolates were very susceptible to the antibiotics tested, except for nalidixic acid. Among 17 strains of Listeria spp., PCR analysis showed that 2 strains of L. monocytogenes isolates proved to have a virulence hly gene, but none of L. innocua had the hly gene. Also, hybridoma Ped-2E9 cells assay showed that only L. monocytogenes isolates killed approximately 95-99％ hybridoma cells after 6 h, but L. innocua isolates had about 0-5％ lethal effect. These results indicate that PCR assay with hly primer or hybridoma Ped-2E9 cells assay could be used as a good monitoring tool or in vitro virulence test for L. monocytogenes.

• Food Science of Animal Resources
• /
• v.34 no.1
• /
• pp.20-25
• /
• 2014

This study evaluated the effects of frankfurter fat content on Listeria monocytogenes resistance to heat stress and gastric fluid, and the Caco-2 cell invasion efficiency of the pathogen. A 10-strain mixture of L. monocytogenes was inoculated on frankfurters formulated with 10%, 20%, and 30% fat content (10%: F10, 20%: F20, 30%: F30) and stored at $10^{\circ}C$ for 30 d. The samples were analyzed for L. monocytogenes resistance to heat stress and a simulated gastric fluid challenge. The total bacteria and L. monocytogenes survival rates were measured on tryptic soy agar plus 0.6% yeast extract and Palcam agar, respectively. L. monocytogenes colonies inoculated on F10, F20, and F30 samples were used for a Caco-2 cell invasion assay. In general, no obvious differences were observed between the survival rates of total bacteria and L. monocytogenes grown on different fat contents under heat stress and gastric fluid challenge. However, L. monocytogenes obtained from the F30 samples had a significantly higher Caco-2 cell invasion efficiency than those in the F10 and F20 samples (p<0.05). These results indicate that although high fat content in food may not be related to L. monocytogenes resistance to heat stress and gastric fluid, it may increase the Caco-2 cell invasion efficiency of the pathogen.

• Korean Journal of Veterinary Service
• /
• v.20 no.1
• /
• pp.69-77
• /
• 1997

To invastigate the epidemiological trait of listeriosis, Listeria monocytogenes were isolated from the carcasses of pigs and cattle, and environmental specimens in slaughter house. Also serotype of isolates were classified by rapid slide agglutination test. In the carcasses of pigs, Listeria sp were isolated from the carcasses after bleeding(62%), after dismemberment(60.0%) and before shipping(76.0%), and L monocytogenes were present in 8% of the carcasses after dismemberment and in 14% of the carcasses before shipping. However, few Listeria sp were isolated from the living body skin and the carcasses after scalding. In the carcasses of cattle, Listeria sp were isolated from the carcasses after bleeding(10%), after dismemberment(36.7%) and before shipping(63.3%), L monocytogenes were present in 3.3% of the carcasses after dismemberment and in 10% of the carcasses before shipping. Overall, L monocytogenes, L innocua, L welshimen, L grayi, and L murrayi were present In 4.8, 40, 2.3, 2.6 and 0.3% of all the carcasses, respectively. Prevalence of Listeria sp in environmental specimens were found to be 80% in slaughter house floors and 100% in sewage, and L monocytogenes were present in 15% of sewage. However, few Listeria sp were isolated from chilled water and from scalding water. Overall, L monocytogenes, L innocua, and L welshimeri were present in 3.8, 45 and 6.3% of all the environmental specimens, respectively. A total 27 strains of L monocytogenes were isolated from samples tested and all of the strains were classified into serotype 1.