Young-Ji Kim

Prevalence and characterization of extended-spectrum-β-lactamase-producing Escherichia coli and Klebsiella pneumoniae in ready-to-eat vegetables

The objective of this investigation was to determine the prevalence and characteristics of extended-spectrum-β-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae in ready-to-eat (RTE) vegetables. A total of 189 RTE vegetable samples (91 sprouts and 98 mixed salads) were collected in a retail market in South Korea from October 2012 to February 2013. The prevalence of ESBL-producing E. coli and K. pneumoniae was 10.1%. Of these, 94.7% were from the sprout samples. All isolates were resistant to cefotaxime, and many of the ESBL producers were also resistant to non-β-lactam antibiotics, including gentamicin, trimethoprim/sulfamethoxazole, and ciprofloxacin (73.7%, 63.2%, and 26.3% respectively). TEM-1, SHV-1, -2, -11, -12, -27, -28 and -61, and CTX-M-14, -15 and -55 β-lactamases were detected alone or in combination. The genetic platforms of all CTX-M producing isolates were ISEcp1-blaCTX-M-orf477 and ISEcp1-blaCTX-M-IS903 in CTX-M groups 1 and 9, respectively. To our knowledge, this is the first report of the prevalence and characterization of ESBL-producing E. coli and K. pneumoniae isolated from RTE vegetables. The results of this study indicate that RTE vegetables, sprouts, in particular, may play a role in spreading antimicrobial resistant bacteria and ESBL genes to humans.

Supplementation of Bolton broth with triclosan improves detection of Campylobacter jejuni and Campylobacter coli in chicken carcass rinse

We compared Bolton enrichment broth supplemented with antimicrobial triclosan (T-Bolton broth) and normal Bolton broth for the isolation of Campylobacter jejuni (C. jejuni) and Campylobacter coli (C. coli) from chicken carcass rinse. Whole chickens were rinsed with buffered peptone water prior to enrichment in normal Bolton broth or T-Bolton broth, followed by inoculation onto modified charcoal-cefoperazone-deoxycholate agar (mCCDA). Suspect colonies were confirmed by PCR. We observed a significantly higher number of C. jejuni or C. coli-positive samples in the T-Bolton broth (71.3%) than in the normal Bolton broth (27.5%) (p<0.05). Furthermore, the number of contaminated mCCDA plates was lower after enrichment in T-Bolton broth (3.8%) than in the normal Bolton broth (75%) (p<0.05), indicating that T-Bolton broth has higher selectivity. Finally, we identified extended-spectrum β-lactamase-producing Escherichia coli as the predominant competing flora in normal Bolton broth. In conclusion, the use of T-Bolton broth results in significant elimination of competing bacteria.

Comparison of Culture, Conventional and Real-time PCR Methods for Listeria monocytogenes in Foods

We compared standard culture methods as well as conventional PCR and real-time PCR for the detection of Listeria monocytogenes (L. monocytogenes) in milk, cheese, fresh-cut vegetables, and raw beef that have different levels of background microflora. No statistical differences were observed in sensitivity between the two selective media in all foods. In total, real-time PCR assay exhibited statistically excellent detection sensitivity (p<0.05) and was less time consuming and laborious as compared with standard culture methods. Conventional culture methods showed poor performance in detecting L. monocytogenes in food with high levels of background microflora, generating numerous false negative results. While the detection of L. monocytogenes in fresh cut vegetable by culture methods was hindered only by L. innocua, various background microflora, such as L. innocua, L. welshimeri, L. grayi, and Enterococcus faecalis appeared on the two selective media as presumptive positive colonies in raw beef indicating the necessity of improvement of current selective media. It appears that real-time PCR is an effective and sensitive presumptive screening tool for L. monocytogenes in various types of foods, especially foods samples with high levels of background microflora, thus complementing standard culture methodologies.

Antimicrobial activity of epigallocatechin gallate from green tea (Camellia sinensis) on pathogenic Salmonella Enteritidis in braised quail eggs

The inhibitory effect of epigallocatechin gallate (EGCG), one of the antioxidants in green tea (Camellia sinensis), against Salmonella Enteritidis was evaluated in commercial braised quail eggs at two temperatures (4 and 25oC). Although S. Enteritidis was dose-dependently suppressed by EGCG in pure culture at 25oC, it was not inhibited in the sauce or eggs at this temperature. At low temperature (4oC), S. Enteritidis was inhibited in both the sauce and eggs by 400 μg/mL EGCG. Thus, EGCG at an appropriate concentration could be a useful food additive for inhibiting S. Enteritidis in braised quail eggs at low temperatures.

Improvement of Karmali Agar by Supplementation with Tazobactam for Detecting Campylobacter in Raw Poultry

In this study, Karmali agar was modified by adding tazobactam (T-Karmali agar) to suppress the growth of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli , which frequently contaminates raw poultry meat. By inoculating 30 Campylobacter spp. strains and 25 ESBL-producing E. coli strains onto Karmali agar and T-Karmali agar containing various concentrations of the antibacterial agent, we determined the optimum concentration of tazobactam to be 4 mg/liter. The Campylobacter spp. isolation rate on T-Karmali agar (13.3%) was higher than that on Karmali agar (8.3%), although the difference was not significant (P > 0.05). However, T-Karmali agar showed a significantly greater selectivity than Karmali agar, as evaluated by comparing the numbers of contaminated agar plates (20.8 versus 82.5%; P < 0.05) and the growth indexes (1.36 versus 2.83) of competing flora. The predominant competing flora on Karmali and T-Karmali agar were identified as ESBL-producing E. coli . Thus, T-Karmali agar might be effective for determining the real prevalence of Campylobacter in raw poultry and, especially, contamination with ESBL-producing E. coli .

Evaluation of Tazobactam-Supplemented, Modified Charcoal-Cefoperazone-Deoxycholate Agar for Qualitative Detection of Campylobacter from Chicken Carcass Rinse

Overgrowth of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli on modified charcoal-cefoperazone-deoxycholate agar (mCCDA) is the most common confounding factor for the isolation of Campylobacter from poultry samples. mCCDA modified by supplementation with tazobactam, an ESBL inhibitor, was evaluated for Campylobacter isolation from chicken carcass rinse with regard to isolation rate and selectivity. In total, 120 whole chicken carcasses purchased from retail stores were rinsed with buffered peptone water enriched with 2× blood-free Bolton broth at 42°C for 48 h and then inoculated onto mCCDA with and without tazobactam supplementation (mCCDA or T-mCCDA) at 42°C for 48 h under microaerobic conditions. Suspect colonies were subcultured and confirmed by colony PCR. Plates with tazobactam exhibited a higher Campylobacter isolation rate (56.7% vs. 30.8%, p < 0.05) and selectivity (0.8 vs. 83.3% plates contaminated with non-Campylobacter, p < 0.05) than mCCDA. Thus, tazobactam-supplemented mCCDA would be a useful option for qualitative detection of Campylobacter in chicken carcass rinse.

Efficacy of Syringe Filtration for the Selective Isolation of Campylobacter from Chicken Carcass Rinse

We investigated the efficacy of syringe filtration for selective isolation of Campylobacter from chicken carcass rinse by combining syringe filtration with the conventional culture method. Whole chicken carcass rinses were incubated in Bolton enrichment broth, set aside or subjected to syringe filtration, and streaked on Campy-Cefex agar with or without cefoperazone antibiotic supplement. Compared with the conventional method without filtration, 0.65-μm-pore-size syringe filtration resulted in a significantly higher number of Campylobacter-positive samples (23.8 to 37.5% versus 70.0 to 72.5%; P < 0.05), a lower number of plates contaminated with non-Campylobacter (93.8% versus 6.3 to 26.3%), and a lower growth index (1 = growth of a few colonies; 2 = growth of colonies on about half of the plate; and 3 = growth on most of the plate) for competing microbiota (2.9 to 3.0 versus 1.2 to 1.4). When syringe filtration was applied, agar plates containing the antibiotic had significantly less contamination (6.3% versus 26.3%; P < 0.05) and a lower growth index (1.2 versus 1.4) compared with plates without the antibiotic, although the Campylobacter isolation rate was similar (P > 0.05). Syringe filtration combined with conventional enrichment improved the rate and selectivity of Campylobacter isolation from chicken carcasses.

Current Status and Prospects of Various Methods used for Screening Probiotic Microorganisms

This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIP)(No. 2015R1A2A2A01005017).

Assessment of Various Factors Influencing the Composition of Cow’s Milk Produced by Organic and Conventional Methods: A Review

Recently, there has been a rapid increase in the sale and purchase of an array of organic products. In particular, organic milk has grown in popularity. This growth could lead to expensive, premium retail prices for various organic cow’s milk products. In fact, most consumers believe that (1) dairy farming to produce organic milk is beneficial for human health and (2) organic milk products are made without the use of various antibiotics, synthetic chemicals, genetic modification, extra hormones, and so on. Several factors, including breed, diet, and stage of lactation, are known to influence the composition of milk. Therefore, this review (1) presents a research outline to compare organic and conventional milk and (2) provides a summary of individual elements that affect the composition of milk.

Evaluation and Determination of Lactase Activity on Various Lactic Acid Bacteria isolated from Kefir by using HPLC

Kefir is a probiotic food. Probiotics have shown to be beneficial to health, and are currently of great interest to the food industry. Hence, this study was carried out to evaluate the lactase activity of kefir-isolated lactic acid bacteria. Three strains, Lactobacillu kefiri DH5 isolated from the kefir grains and Bifidobacterium animalis subsp. Lactis and Bifidobacteria longum 720, commercial probiotic LAB, were fermented in 10% reconstituted nonfat dry milk suspensions and incubated at 37°C for 48 h, and then analyzed for various saccarides by HPLC. The results showed that changes in the concentrations of lactose and galactose were significantly decreased and increased, respectively (p<0.05), but all 3 probiotic strains tested in this study showed no increase in glucose concentration during 48 h of incubation. Both DH5 and BL720 showed high lactase activities (p<0.05), whereas BLC exhibited the lowest activity. Additionally, all three lactic acid bacteria showed high tagatose, but did not show high xylose and sedoheptulose. Finally, DH5, a kefir-isolated LAB, may have similar characteristics and properties to typical Bifidobacterium spp. and showed higher lactase activity than commercial Bifidobacterium spp.