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.

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.

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