Nari Lee

Occurrence of toxigenic Staphylococcus aureus in ready-to-eat food in Korea

Toxigenic Staphylococcus aureus contamination in ready-to-eat (RTE) food is a leading cause of foodborne illness in Korea. To monitor food contamination by S. aureus, a total of 3332 RTE food samples were selected from nationwide wholesale marts between 2003 and 2004 and examined. A total of 285 (8.6%) of the overall samples were contaminated by S. aureus. According to the analysis, 31.6% of the tested cream-cakes, 19.8% of the raw fish, and 19.3% of the rice cakes with filling were contaminated with S. aureus. Forty-seven percent of the strains isolated from the contaminated food were enterotoxigenic S. aureus. The phenotypic result of the strain isolated from food showed that 48% of the strains produced one or more toxins, such as staphylococcal enterotoxins A, B, and C (SEA, SEB, and SEC). At least one SEA was produced by over 90% of the toxigenic strains. Other toxins, such as SEB, SEC, SED, SEA+SEC, and SEC+SED, were each detected. Toxic shock syndrome toxin 1 (TSST-1), a causative agent of toxic shock syndrome, was detected in 13 strains of the toxigenic isolates from the food. As the result of genotyping, 22 strains with a toxin gene that was not detected in the phenotypic analysis were also detected. Sixty-nine percent of the toxigenic strains had at least one sea gene, and the most prevalent genotype was sea+seh (34.4%), followed by sea (18.8%) and sea+seg+sei (15.6%). The tst gene encoding TSST-1 was found in 13 strains (13.5%). The genes (eta and etb) encoding exfoliative toxins A and B were not detected in any of the samples.

Microbiological Quality of Fresh-Cut Produce and Organic Vegetables

This study was performed to assess the microbiological quality and potential health risk of fresh-cut produce and organic vegetables sampled from supermarkets and department stores in Korea. A total of 96 samples comprised three types of fresh-cut produce (sprouts, mixed-vegetables, fruit) and three types of organic vegetables (lettuce, perilla leaf, green pepper). The samples were analyzed for total viable cell counts, coliforms, Enterobacteriaceae, Escherichia coli, Salmonella spp., Listeria monocytogenes, Vibrio parahaemolyticus, Bacillus cereus, and Staphylococcus aureus. The microbiological counts of fruit were very low. Sprouts were highly contaminated by total viable cell counts (8.3±0.57 log CFU/g), Enterobacteriaceae (7.1±0.76 log CFU/g), and coliforms (4.9±0.40 log MPN/g), and showed a high incidence level of B. cereus (2.9±0.48 log CFU/g). Of the fresh-cut produce analyzed, six (13.6%) mixed-vegetable salads were E. coli positive. S. aureus was detected in only one sprout sample and one mixed-vegetable salad, and its contamination levels were under 2 log CFU/g, which is appropriate for Korean standards (＜3 log CFU/g) of fresh-cut produce. Of the organic vegetables, lettuces were highly contaminated by total viable cell counts (6.4±0.74 log CFU/g), Enterobacteriaceae (5.7±0.98 log CFU/g), and coliforms (3.7±1.72 log MPN/g). Two (13.6%) organic lettuce and one (7.1%) perillar leaf sample were E. coli positive, and S. aureus was detected in one lettuce and two perilla leaf samples. Salmonella spp., Vibrio parahaemolyticus, and Listeria monocytogenes were not detected in any of the fresh-cut produce or organic vegetables analyzed.

Screening of Korean medicinal plants for possible osteoclastogenesis effects in vitro.

Bone undergoes continuous remodeling through bone formation and resorption, and maintaining the balance for skeletal rigidity. Bone resorption and loss are generally attributed to osteoclasts. Differentiation of osteoclasts is regulated by receptor activator of nuclear factor NF-kB ligand (RANKL), a member of tumor necrosis factor family. When the balance is disturbed, pathological bone abnormality ensues. Through the screening of traditional Korean medicinal plants, the effective molecules for inhibition and stimulation of RANKL-induced osteoclast differentiation in mouse bone marrow macrophages were identified. Among 222 methanol extracts, of medicinal plants, 10 samples exhibited ability to induce osteoclast differentiation. These include Dryobalanops aromatica, Euphoria longana, Lithospermum erythrorhizon, Prunus mume, Prunus nakaii, and Polygonatum odoratum. In contrast, Ailanthus altissima, Curcuma longa, Solanum nigrum, Taraxacum platycarpa, Trichosanthes kirilowii, and Daphne genkwa showed inhibitory effects in RANKL-induced osteoclast differentiation.

Genetic Diversity, Antimicrobial Resistance, and Toxigenic Profiles of Bacillus cereus Strains Isolated from Sunsik

Bacillus cereus can cause emetic and diarrheal types of food poisoning, but little study has been done on the toxins and toxin-encoding genes of B. cereus strains isolated from Sunsik, a Korean ready-to-eat food prepared from grains, fruits, and vegetables. In this study, 39 unique B. cereus strains were isolated and identified from Sunsik samples, with an average contamination level of 10 to 200 CFU/g. The detection rates of the hblACD, cytK, and bceT genes among all the strains were 48.7, 66.7, and 87.1%, respectively. All 39 B. cereus strains carried nheABC and entFM genes, and 36 strains also had the ces gene, which encodes an emetic toxin. Nonhemolytic enterotoxin and hemolysin BL enterotoxin were produced by 39 and 26 strains, respectively. The strains were separated into 13 profiles based on the presence or absence of toxins and their genes, as determined by antibody tests and PCR analysis. Profile 1 was the largest group, comprising 30.7% (12 of 39) of the B. cereus strains tested; these strains harbored all toxins and their genes. The B. cereus strains were susceptible to most of the antibiotics tested but were highly resistant to b -lactam antibiotics. The repetitive element sequence polymorphism PCR fingerprints of the B. cereus strains were not influenced by the presence of toxin genes or antibiotic resistance profiles. Our results suggest that B. cereus strains from Sunsik could cause either the diarrheal or emetic types of food poisoning because all strains isolated contained at least one toxin and its gene, although the level of B. cereus contamination in Sunsik was low.

High-performance sub-terahertz transmission imaging system for food inspection

Unlike X-ray systems, a terahertz imaging system can distinguish low-density materials in a food matrix. For applying this technique to food inspection, imaging resolution and acquisition speed ought to be simultaneously enhanced. Therefore, we have developed the first continuous-wave sub-terahertz transmission imaging system with a polygonal mirror. Using an f-theta lens and a polygonal mirror, beam scanning is performed over a range of 150 mm. For obtaining transmission images, the line-beam is incorporated with sample translation. The imaging system demonstrates that a pattern with 2.83 mm line-width at 210 GHz can be identified with a scanning speed of 80 mm/s.

Simple high-performance liquid chromatography method for the simultaneous analysis of aflatoxins, ochratoxin A, and zearalenone in dried and ground red pepper.

Aflatoxins B1, B2, G1, G2 (AFB1, AFB2, AFG1, AFG2), ochratoxin A (OTA), and zearalenone (ZEA) in dried and ground red pepper (Capsicum annuum) were simultaneously analyzed with high-performance liquid chromatography coupled to fluorescence detection after post-column derivatization. The analytical method was validated for specificity, selectivity, linearity, limits of detection and quantification, recovery, precision, and measurement of uncertainty. The limits of detection and quantification were 0.10 and 0.25 μg/kg for AFB1, 0.04 and 0.06 μg/kg for AFB2, 0.14 and 0.50 μg/kg for AFG1, 0.05 and 0.10 μg/kg for AFG2, 0.12 and 0.45 μg/kg for OTA, and 4.00 and 13.25 μg/kg for ZEA, respectively. The average recoveries ranged from 80.4 to 98.5% for different concentrations of AFB1, AFB2, AFG1, AFG2, OTA, and ZEA in spiked samples. The measurement uncertainties were 0.64 to 1.62 μg/kg for AFB1, 0.24 to 0.45 μg/kg for AFB2, 0.79 to 2.19 μg/kg for AFG1, 0.32 to 0.61 μg/kg for AFG2, 0.81 to 2.31 μg/kg for OTA, and 8.48 to 26.25 μg/kg for ZEA. This method was successfully applied for the simultaneous determination of mycotoxins for 78 red peppers collected from Korean and Indian markets. Aflatoxins (sum of AFB1, AFB2, AFG1, and AFG2) were detected in 2% of nonpacked samples (n = 23) and 43% of packed samples (n = 55), at levels of 0.04 to 38.03 μg/kg. OTA was detected in 4% of nonpacked samples and 48% of packed samples, at levels of 0.15 to 56.30 μg/kg. ZEA was not detected in any samples. These findings indicate that the analytical method described here is suitable for the routine determination of the amounts of AFs, OTA, and ZEA in dried and ground red pepper.

Occurrence of aflatoxin and aflatoxigenic Aspergillus species in corn harvested in Korea

Sixty six corn samples freshly harvested in Korea were analyzed for the occurrence of aflatoxin and aflatoxigenic Aspergillus using chromatographic and multiplex polymerase chain reaction (PCR) methods. Aflatoxin and aflatoxigenic Aspergillus were detected in 13.6% (0.02 to 0.48 μg kg−1) and 3.0% of the corn samples, respectively. Aflatoxigenic Aspergillus isolates and A. flavus KCCM60330 showed high similarity (98–98.8%). These results suggest that occurrence of aflatoxin and aflatoxigenic Aspergillus in corn harvested from Korea is low.

Rapid Detection of Escherichia coli O157:H7 in Fresh Lettuce Based on Localized Surface Plasmon Resonance Combined with Immunomagnetic Separation

This study presents a method for rapid detection of Escherichia coli O157:H7 in fresh lettuce based on the properties of target separation and localized surface plasmon resonance of immunomagnetic nanoparticles. The multifunctional immunomagnetic nanoparticles enabling simultaneous separation and detection were prepared by synthesizing magnetic nanoparticles (ca. 10 nm in diameter) composed of an iron oxide (Fe3O4) core and gold shell and then conjugating these nanoparticles with the anti- E. coli O157:H7 antibodies. The application of multifunctional immunomagnetic nanoparticles for detecting E. coli O157:H7 in a lettuce matrix allowed detection of the presence of <1 log CFU mL-1 without prior enrichment. In contrast, the detection limit of the conventional plating method was 2.74 log CFU mL-1. The method, which requires no preenrichment, provides an alternative to conventional microbiological detection methods and can be used as a rapid screening tool for a large number of food samples.