[Analysis of Maximum Growth Rate and Construction of Predictive Growth Model for Bacillus cereusin Mashed Potato by Calorimetric Method].

The maximum growth rate (µmax) of Bacillus cereus was estimated using a non-destructive isothermal calorimetric method, and a growth prediction model was constructed based on the measurement results. SCD medium and mashed potato were inoculated with serial-diluted inoculum of B. cereus. Heat generation curves were determined using an isothermal calorimeter at 35, 25, and 15℃. The µmax was determined from the relationship between the increase in B. cereus cell number and incubation time, which was detected through the heat generation of the B. cereus biological process. Moreover, the growth prediction model was constructed using Ratkowsky's square-root model. The results of the growth prediction model based on the data of the calorimetric and conventional culture methods for SCD were expressed as √µCalmax=0.0354 (T-4.9)[R2=0.99] and √µCCMmax=0.0335 (T-5.0)[R2=0.99]; a similar equation was provided by both methods. Conversely, the results of the growth prediction model based on the calorimetric method data for mashed potato were given as √µCalmax=0.0390 (T-8.5)[R2=0.99]; the maximum growth rates at 30 and 20℃ were predicted as 0.70 and 0.20 (1/hr), respectively. The maximum growth rates obtained using the conventional culture method were 0.63 and 0.29 (1/hr), respectively, similar to the calorimetric method results. The predictive microbiological analysis using the calorimetric method enabled the rapid provision of a growth prediction equation, and the number of samples could be substantially reduced compared with that for the conventional culture method.

Predictive Growth Model of Listeria monocytogenes Under Fluctuating Temperature Conditions in Pasteurized Milk by Using Real-Time Polymerase Chain Reaction.

The aim of this study was to evaluate the application of real-time polymerase chain reaction (PCR)-based quantification as a rapid and accurate tool for the monitoring and prediction of Listeria monocytogenes growth in pasteurized milk under constant and fluctuating temperature conditions. The growth of L. monocytogenes was monitored under constant temperature conditions at 4°C, 10°C, 15°C, 20°C, and 35°C. High correlation was obtained between the bacterial growth rate and incubation temperature, where the R2 of the slope of the square root model was calculated to be 0.993 and 0.996 for real-time PCR and the conventional culture method, respectively. Moreover, the obtained maximum specific growth rate (µmax) data plots were correlated with 188 L. monocytogenes µmax data points from the existing model according to ComBase database, with an R2 of 0.961 for real-time PCR and of 0.931 for the conventional culture method. The growth models were examined under three different patterns of fluctuating temperature conditions ranging from 2°C to 30°C. The prediction results fell within ±20% of the relative error zone, showing that real-time PCR quantification could be used for fast, sensitive, and specific bacterial growth monitoring with high-throughput results. Real-time PCR should be considered a promising option and powerful tool for the construction of a bacterial growth prediction model for safety risk analysis in the dairy industry.

Predictive Modeling for the Growth of Salmonella Enteritidis in Chicken Juice by Real-Time Polymerase Chain Reaction.

The goals of this study were to monitor the growth kinetics of Salmonella Enteritidis in chicken juice using real-time polymerase chain reaction (PCR) and to evaluate its efficacy by comparing the results with an experimental database. Salmonella Enteritidis was inoculated in chicken juice samples at an initial inoculum of 104 CFU/mL with inoculated samples incubated at six different temperatures (10, 15, 20, 25, 30, and 35°C). Sampling was carried out for 36 h to observe the growth of Salmonella Enteritidis. The total DNA was extracted from the samples, and the copy number of the Salmonella invasion gene (invA) was quantified by real-time PCR and converted to Salmonella Enteritidis cell concentration. Growth kinetics data were analyzed by the Baranyi and Roberts model to obtain growth parameters, whereas the Ratkowsky's square-root model was used to describe the effect of the interactions between growth parameters and temperature on the growth of Salmonella Enteritidis. The growth parameters of Salmonella Enteritidis obtained from an experiment conducted at a constant temperature were validated with growth data from chicken juice samples that were incubated under fluctuating temperature conditions between 5°C and 30°C for 30-min periods. A high correlation was observed between maximum growth rate (µmax) and storage temperature, indicating that the real-time PCR-monitoring method provides a precise estimation of Salmonella Enteritidis growth in food material with a microbial flora. Moreover, the µmax data reflected data from microbial responses viewer database and ComBase. The results of this study suggested that real-time PCR monitoring provides a precise estimation of Salmonella Enteritidis growth in food materials with a background microbial flora.

Microbioligical Hazard Contamination in Fermented Vegetables Sold in Local Markets in Cambodia.

　Fermented vegetables are common part of Cambodian diet. The food safety status for these foods has not been investigated. This study was conducted to evaluate the microbiological hazards that contaminated fermented vegetables. A total of 68 samples of fermented vegetables were purchased randomly from five wet markets in Phnom Penh. The conventional culture methods for microbiological analysis were used. Coliform bacteria (Escherichia coli, Cronobactersakazakii, and Enterobacter spp.), opportunistic non-Entrobacteriaceae, Enterococcus spp., Staphylococcus spp., and Listeria spp. were found in these fermented foods. The highest contamination rate of Enterococcus spp. was 34% of total fermented vegetable samples, followed by Bacillus spp. coliform bacteria and E. coli (31%, 24% and 10%, respectively). The potential foodborne pathogen, C. sakazakii, was identified in one sample. Fermented mixed vegetables showed higher contamination rate of coliform bacteria (50%) than fermented single-type vegetables (13%). The results showed that fermented vegetables sold in wet market are poor in hygiene. The stage in the processing chain where contamination occurred should be identified and basic sanitary practice should be enforced to improve the food safety of fermented vegetables in Cambodia.

Fate of Escherichia coli O157 Cells Inoculated into Lightly Pickled Chinese Cabbage during Processing, Storage and Incubation in Artificial Gastric Juice.

Fate of Escherichia coli O157 cells was evaluated when inoculated into each step after production of lightly pickled Chinese cabbage. The efficacy of surface sterilization by 100 mg/L of chlorine water for 10 min on raw leaves (6.0 log CFU/g) was 2.2 log CFU/g reduction. No meaningful change of the population of E. coli O157 (3.5 log CFU/g to 1.5 log MPN/g) contaminated into 19 kinds of products was observed. These results indicated the difficulty of estimating the viable count of the cells between contaminated on farms and further processing and storage steps. The population of E. coli O157 (3 log CFU/g to 1 log MPN/g) inoculated into the Chinese cabbage products was reduced less than 0.6 log CFU/g after 2 h-incubation at 37℃ in artificial gastric juice. Prevention from initial contamination of E. coli O157 on the ingredients of Chinese cabbage products is important to reduce the risk of food poisoning because the reduction of the bacterial counts after processing and consumption are limited.

Survival of Inoculated Escherichia coli O157:H7 in Japanese Sweet Dumplings during Storage.

An outbreak of Escherichia coli O157:H7 occurred due to the consumption of sweet dumplings in Japan. We examined the survival of E. coli O157:H7 inoculated into several types of sweet dumplings to evaluate the progress of the residual contaminating pathogens after the production or packing processes. For all 4 types of tested typical sweet dumplings, no significant reduction in the viable cell counts of inoculated E. coli O157:H7 (3 log CFU/g) was observed during storage at -20 ℃ and 5 ℃ for 5 weeks. Approximately 1 log CFU/g of reduction was observed after storage for 5 weeks at 10 ℃ and 15 ℃, which corresponded to the growth of the naturally contaminating fungi. Similar results were obtained when we used several types of commercially distributed sweet dumplings. It is of vital importance to prevent the cross contamination of sweet dumplings after the heating process in order to reduce the risk of foodborne illness.

Prevalence of foodborne pathogens in retailed foods in Thailand.

The consumption of foodborne pathogens contaminated in food is one of the major causes of diarrheal diseases in Thailand. The objective of this study was to evaluate the prevalence and types of contaminating bacteria in retailed foodstuffs in Thailand. Food from four categories (137 samples total), including meat (51 samples), vegetables (38 samples), fish or seafood (37 samples), and fermented food (11 samples), was purchased randomly from seven different open-markets and seven supermarkets in Thailand from August 2010 to March 2011. Seven types of major foodborne pathogens were identified using conventional culture methods. Approximately 80% of meat samples tested was contaminated with Salmonella spp. In contrast, the Salmonella spp. contamination rate of vegetable (5%) or fermented food (9%) samples was comparatively low. Six strains of Cronobacter sakazakii and two strains of Yersinia enterocolitica were also isolated. A substantially higher rate of contamination by Bacillus cereus was observed in fermented food (82%) than in samples of meat (2%) and fish or seafood (5%). Seven Listeria spp. isolates were obtained from meat and fish or seafood samples. Approximately 39% of samples tested were found to be contaminated with Staphylococcus spp. (54 isolates). The rate of bacterial contamination of meat did not depend on the type of market. However, the contamination rate of Staphylococcus spp. in vegetables was higher in open markets than in supermarkets, and the contamination rate of Salmonella spp. and Staphylococcus spp. in fish or seafood samples purchased in open markets was likewise higher than in those purchased in supermarkets. Therefore, improvement of hygienic practices throughout the food chain may be required to reduce the risk of food poisoning.