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.

Multiplex PCR assay and lyophilization for detection of Salmonella spp., Staphylococcus aureus and Bacillus cereus in pork products.

Multiplex PCR (m-PCR) has the potential for more rapid detection of pathogens compared to simple PCR through the simultaneous amplification of multiple gene targets using several sets of specific primers. Here, we developed an m-PCR assay which combined dry reagent mixtures for ready-to-use simultaneous detection of Salmonella spp., Bacillus cereus, and Staphylococcus aureus. The assay did not show cross-reactivity with several common bacterial pathogens and the detection limit was 103 CFU/mL for mixed genomic DNA in pure culture. Lyophilized m-PCR reagents are stable for 2 months stored at 4 °C and for 1 month stored at 25 °C. Detection sensitivities of both dry and fresh mixes were able to simultaneously detect 10 CFU/mL of each pathogen in artificially inoculated samples after enrichment for 6 and 12 h. Results demonstrated that this method is both sensitive and specific and can be used for rapid detection and differentiation of foodborne diseases.

Bacterial Contamination into Ready-to-Eat Foods Sold in Middle Thailand.

　Bacterial contamination in ready-to-eat (RTE) foods prepared and sold by small businesses in middle Thailand was surveyed. The 135 samples were randomly purchased from open markets and supermarkets in Bangkok and Pathum Thani provinces during May 2013 to February 2015. The results indicated that the rate of contamination in cooked pork, chicken meat and cooked aquatic items were 13/39 (33%), 18/45 (40%) and 14/57 (25%), respectively and the rate of bacterial contamination of collected samples from open market and supermarket were 26/67 (39%) and 19/68 (27%), respectively. Therefore, no statistically significant difference of contamination rate between two kinds of market or among three categories of food. The most contaminated pathogenic bacteria was Staphylococcus aureus 27/135 (20%) while that of Salmonella spp. was the lowest 5/135 (4%) in each categories of collected food samples. Implementation of suitable hygienic practices in the small food businesses are thought to be required to reduce the risk of foodborne illnesses caused by the consumption of RTE foods sold in middle Thailand.

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.

Yersinia enterocolitica: Epidemiological Studies and Outbreaks.

Yersinia enterocolitica is the most common bacteriological cause of gastrointestinal disease in many developed and developing countries. Although contaminated food is the main source of human infection due to Y. enterocolitica, animal reservoir and contaminated environment are also considered as other possible infection sources for human in epidemiological studies. Molecular based epidemiological studies are found to be more efficient in investigating the occurrence of human pathogenic Y. enterocolitica in natural samples, in addition to conventional culture based studies.