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Effects of cold storage and heat-acid shocks on growth and verotoxin 2production of Escherichia coli O157 : H7

机译：Effects of cold storage and heat-acid shocks on growth and verotoxin 2production of Escherichia coli O157 : H7

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Escherichia coli 0157:H7 was cold-stored (4 degrees C) either in nutritious menstruum buffered Brain Heart Infusion (BHI) broth or with starvation (buffered saline) at pH 7.0 or 5.5. Cultures grown in BHI broth at 37 degrees C for 24h served as non-cold-stored controls. After LF-weeks cold storage, bacterial cells were shocked by heat (45 degrees C for 5 min) and acid (pH 2.5 for 30 min at 37 degrees C) and subsequently moved to optimal conditions (BHI broth of pH 7.4 incubated at 37 degrees C). The results showed: (a) both lag-phase duration and growth rate of this pathogen at 37 degrees C significantly increased after cold-storage with starvation, but not after cold storage in the nutritious menstruum; (b) combined heat-acid shocks increased growth rates at 37 degrees C of both previously cold-stored and non-cold-stored bacterial cells; (c) final concentrations of verotoxin produced by bacterial cells at 37 degrees C were not affected by previous cold storage in the nutritious menstruum; (d) verotoxin production by bacterial cells at 37 degrees C increased after cold storage with starvation, and heat-acid shocks further enhanced that production. Further research is needed to evaluate the food safety implications of these results, i.e. whether cells of E. coli 0157:H7 originating from nutrient-poor/lower-pH environments may be more harmful to humans than those from nutrient-rich/higher-pH foods.

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