Jimyeong Ha

Clinical relevance of infections with zoonotic and human oral species of Campylobacter

Genus Campylobacter has been recognized as a causative bacterial agent of animal and human diseases. Human Campylobacter infections have caused more concern. Campylobacters can be classified into two groups in terms of their original host: zoonotic and human oral species. The major zoonotic species are Campylobacter jejuni and Campylobacter coli, which mostly reside in the intestines of avian species and are transmitted to humans via consumption of contaminated poultry products, thus causing human gastroenteritis and other diseases as sequelae. The other campylobacters, human oral species, include C. concisus, C. showae, C. gracilis, C. ureolyticus, C. curvus, and C. rectus. These species are isolated from the oral cavity, natural colonization site, but have potential clinical relevance in the periodontal region to varying extent. Two species, C. jejuni and C. coli, are believed to be mainly associated with intestinal diseases, but recent studies suggested that oral Campylobacter species also play a significant role in intestinal diseases. This review offers an outline of the two Campylobacter groups (zoonotic and human oral), their virulence traits, and the associated illnesses including gastroenteritis.

Invited review: Microbe-mediated aflatoxin decontamination of dairy products and feeds

Aspergillus flavus, Aspergillus parasiticus, and Aspergillus nomius contaminate corn, sorghum, rice, peanuts, tree nuts, figs, ginger, nutmeg, and milk. They produce aflatoxins, especially aflatoxin B1, which is classified as a Group 1 carcinogen by the International Agency for Research on Cancer. Many studies have focused on aflatoxin removal from food or feed, especially via microbe-mediated mechanisms-either adsorption or degradation. Of the lactic acid bacteria, Lactobacillus rhamnosus GG efficiently binds aflatoxin B1, and a peptidoglycan in the bacterium cell wall plays an important role. This ability of L. rhamnosus GG should be applied to the removal of aflatoxin B1. Aflatoxin can be removed using other aflatoxin-degrading microorganisms, including bacterial and fungal strains. This review explores microbe-associated aflatoxin decontamination, which may be used to produce aflatoxin-free food or feed.

Probabilistic models to describe the effect of NaNO2 in combination with NaCl on the growth inhibition of Lactobacillus in frankfurters.

Probabilistic models were developed to describe the antimicrobial effect of NaNO2 (0-210 ppm) in combination with NaCl (0-1.75%) on Lactobacillus growth under aerobic and anaerobic conditions. Growth (1) or no growth (0) was assessed every 24h as turbid or not turbid, respectively. The growth response data were analyzed by logistic regression to select significant variables (P<0.05) for Lactobacillus growth inhibition, and these variables were used to generate a probabilistic model. The model was then validated with observed data from frankfurters (a model system). NaNO2 and NaCl inhibited (P<0.05) Lactobacillus growth at all temperatures under aerobic and anaerobic conditions, and the antimicrobial effect of NaNO2 increased as the NaCl concentration increased. Validation showed that the performance of the developed model was appropriate. These results indicate that the models developed in this study should be useful for describing the antimicrobial effect of NaNO2 in combination with NaCl on Lactobacillus.

Probabilistic Models to Predict Listeria monocytogenes Growth at Low Concentrations of NaNO2 and NaCl in Frankfurters

This study developed probabilistic models to describe Listeria monocytogenes growth responses in meat products with low concentrations of NaNO2 and NaCl. A five-strain mixture of L. monocytogenes was inoculated in NBYE (nutrient broth plus 0.6% yeast extract) supplemented with NaNO2 (0-141 ppm) and NaCl (0-1.75%). The inoculated samples were then stored under aerobic and anaerobic conditions at 4, 7, 10, 12, and 15℃ for up to 60 d. Growth response data [growth (1) or no growth (0)] for each combination were determined by turbidity. The growth response data were analyzed using logistic regression to predict the growth probability of L. monocytogenes as a function of NaNO2 and NaCl. The model performance was validated with the observed growth responses. The effect of an obvious NaNO2 and NaCl combination was not observed under aerobic storage condition, but the antimicrobial effect of NaNO2 on the inhibition of L. monocytogenes growth generally increased as NaCl concentration increased under anaerobic condition, especially at 7-10℃. A single application of NaNO2 or NaCl significantly (p<0.05) inhibited L. monocytogenes growth at 4-15℃, but the combination of NaNO2 or NaCl more effectively (p<0.05) inhibited L. monocytogenes growth than single application of either compound under anaerobic condition. Validation results showed 92% agreement between predicted and observed growth response data. These results indicate that the developed model is useful in predicting L. monocytogenes growth response at low concentrations of NaNO2 and NaCl, and the antilisterial effect of NaNO2 increased by NaCl under anaerobic condition.

Quantitative Microbial Risk Assessment for Campylobacter Foodborne Illness in Raw Beef Offal Consumption in South Korea

This study evaluated the risk of Campylobacter foodborne illness caused by the intake of raw beef offal in South Korea. The prevalence of Campylobacter spp. in raw beef offal (liver and tripe) was investigated by plating samples on modified charcoal-cefoperazone-deoxycholate agar with Preston enrichment broth. Data were collected about storage temperature and length of storage of raw beef offal, and probabilistic distributions for the data were determined, using @RISK software. Predictive models were developed to describe the fate of Campylobacter in raw beef offal, and the amount and frequency of consumption and dose-response model were surveyed. Subsequently, these data were used to estimate the risk of Campylobacter foodborne illness caused by the intake of raw beef offal. Of 80 beef offal samples, 1 (1.25%) was contaminated with Campylobacter jejuni . Predictive models were used for exposure assessment. An exponential distribution was selected to represent beef offal consumption by people who eat this occasionally, with a mean of 60.2 g and 3.6% monthly consumption frequency. Simulations using @RISK predicted that the probability of Campylobacter foodborne illness per person per month is 1.56 × 10-5 for home consumption and 1.74 × 10-5 for restaurant consumption in South Korea, which indicates the risk of Campylobacter foodborne illness by intake of raw beef offal in South Korea.

Quantitative Microbial Risk Assessment for Campylobacter spp. on Ham in Korea

The objective of this study was to evaluate the risk of illness from Campylobacter spp. on ham. To identify the hazards of Campylobacter spp. on ham, the general characteristics and microbial criteria for Campylobacter spp., and campylobacteriosis outbreaks were investigated. In the exposure assessment, the prevalence of Campylobacter spp. on ham was evaluated, and the probabilistic distributions for the temperature of ham surfaces in retail markets and home refrigerators were prepared. In addition, the raw data from the Korea National Health and Nutrition Examination Survey (KNHNES) 2012 were used to estimate the consumption amount and frequency of ham. In the hazard characterization, the Beta-Poisson model for Campylobacter spp. infection was used. For risk characterization, a simulation model was developed using the collected data, and the risk of Campylobacter spp. on ham was estimated with @RISK. The Campylobacter spp. cell counts on ham samples were below the detection limit (<0.70 Log CFU/g). The daily consumption of ham was 23.93 g per person, and the consumption frequency was 11.57%. The simulated mean value of the initial contamination level of Campylobacter spp. on ham was −3.95 Log CFU/g, and the mean value of ham for probable risk per person per day was 2.20×10−12. It is considered that the risk of foodborne illness for Campylobacter spp. was low. Furthermore, these results indicate that the microbial risk assessment of Campylobacter spp. in this study should be useful in providing scientific evidence to set up the criteria of Campylobacter spp..

Microbial Risk Assessment of Non-Enterohemorrhagic Escherichia coli in Natural and Processed Cheeses in Korea

This study assessed the quantitative microbial risk of non-enterohemorrhagic Escherichia coli (EHEC). For hazard identification, hazards of non-EHEC E. coli in natural and processed cheeses were identified by research papers. Regarding exposure assessment, non-EHEC E. coli cell counts in cheese were enumerated, and the developed predictive models were used to describe the fates of non-EHEC E. coli strains in cheese during distribution and storage. In addition, data on the amounts and frequency of cheese consumption were collected from the research report of the Ministry of Food and Drug Safety. For hazard characterization, a dose-response model for non-EHEC E. coli was used. Using the collected data, simulation models were constructed, using software @RISK to calculate the risk of illness per person per day. Non-EHEC E. coli cells in natural- (n=90) and processed-cheese samples (n=308) from factories and markets were not detected. Thus, we estimated the initial levels of contamination by Uniform distribution × Beta distribution, and the levels were −2.35 and −2.73 Log CFU/g for natural and processed cheese, respectively. The proposed predictive models described properly the fates of non-EHEC E. coli during distribution and storage of cheese. For hazard characterization, we used the Beta-Poisson model (α=2.21×10−1, N50=6.85×107). The results of risk characterization for non-EHEC E. coli in natural and processed cheese were 1.36×10−7 and 2.12×10−10 (the mean probability of illness per person per day), respectively. These results indicate that the risk of non-EHEC E. coli foodborne illness can be considered low in present conditions.

The Correlation between NaCl Adaptation and Heat Sensitivity of Listeria monocytogenes, a Foodborne Pathogen through Fresh and Processed Meat

This study examined the relationship between NaCl sensitivity and stress response of Listeria monocytogenes. Nine strains of L. monocytogenes (NCCP10805, NCCP10806, NCCP10807, NCCP10808, NCCP10809, NCCP10810, NCCP10811, NCCP10920 and NCCP 10943) were exposed to 0%, 1%, 2% and 4% NaCl, and then incubated at 60℃ for 60 min to select strains that were heat-sensitized (HS) and non-sensitized (NS) by NaCl exposure. After heat challenge, L. monocytogenes strains were categorized as HS (NCCP 10805, NCCP10806, NCCP10807, NCCP10810, NCCP10811 and NCCP10920) or NS (NCCP10808, NCCP10809 and NCCP10943). Total mRNA was extracted from a HS strain (NCCP10811) and two NS strains (NCCP10808 and NCCP10809), and then cDNA was prepared to analyze the expression of genes (inlA, inlB, opuC, betL, gbuB, osmC and ctc) that may be altered in response to NaCl stress, by qRT-PCR. The expression levels of two invasion-related genes (inlA and inlB) and two stress response genes (opuC and ctc) were increased (p<0.05) in NS strains after NaCl exposure in an NaCl concentration-dependent manner. However, only betL expression was increased (p<0.05) in the HS strains. These results indicate that the effect of NaCl on heat sensitization of L. monocytogenes is strain dependent and that opuC and ctc may prevent NS L. monocytogenes strains from being heat sensitized by NaCl. Moreover, NaCl also increases the expression of invasion-related genes (inlA and inlB).

Kinetic Behavior of Salmonella on Low NaNO2 Sausages during Aerobic and Vacuum Storage.

This study evaluated the growth kinetics of Salmonella spp. in processed meat products formulated with low sodium nitrite (NaNO2). A 5-strain mixture of Salmonella spp. was inoculated on 25-g samples of sausages formulated with sodium chloride (NaCl) (1.0%, 1.25%, and 1.5%) and NaNO2 (0 and 10 ppm) followed by aerobic or vacuum storage at 10℃ and 15℃ for up to 816 h or 408 h, respectively. The bacterial cell counts were enumerated on xylose lysine deoxycholate agar, and the modified Gompertz model was fitted to the Salmonella cell counts to calculate the kinetic parameters as a function of NaCl concentration on the growth rate (GR; Log CFU/g/h) and lag phase duration (LPD; h). A linear equation was then fitted to the parameters to evaluate the effect of NaCl concentration on the kinetic parameters. The GR values of Salmonella on sausages were higher (p<0.05) with 10 ppm NaNO2 concentration than with 0 ppm NaNO2. The GR values of Salmonella decreased (p<0.05) as NaCl concentration increased, especially at 10℃. This result indicates that 10 ppm NaNO2 may increase Salmonella growth at low NaCl concentrations, and that NaCl plays an important role in inhibiting Salmonella growth in sausages with low NaNO2.

Evaluation of Salmonella Growth at Low Concentrations of NaNO 2 and NaCl in Processed Meat Products Using Probabilistic Model

This study developed probabilistic models to predict Salmonella growth in processed meat products formulated with varying concentrations of NaCl and NaNO2. A five-strain mixture of Salmonella was inoculated in nutrient broth supplemented with NaCl (0%, 0.25%, 0.5%, 0.75%, 0.5%, 1.0%, 1.25%, and 1.75%) and NaNO2 (0, 15, 30, 45, 60, 75, 90, 105, and 120 ppm). The inoculated samples were then incubated under aerobic and anaerobic conditions at 4°C, 7°C, 10°C, 12°C, and 15°C for up to 60 days. Growth (assigned the value of 1) or no growth (assigned the value of 0) for each combination was evaluated by turbidity. These growth response data were analyzed with a logistic regression to evaluate the effect of NaCl and NaNO2 on Salmonella growth. The results from the developed model were compared to the observed data obtained from the frankfurters to evaluate the performance of the model. Results from the developed model showed that a single application of NaNO2 at low concentrations did not inhibit Salmonella growth, whereas NaCl significantly (p<0.05) inhibited Salmonella growth at 10°C, 12°C, and 15°C, regardless of the presence of oxygen. At 4°C and 7°C, Salmonella growth was not observed in either aerobic or anaerobic conditions. When NaNO2 was combined with NaCl, the probability of Salmonella growth decreased. The validation value confirmed that the performance of the developed model was appropriate. This study indicates that the developed probabilistic models should be useful for describing the combinational effect of NaNO2 and NaCl on inhibiting Salmonella growth in processed meat products.