2D-LC/MS/MS analysis of Escherichia coli during exposure an abrupt downshift in water activity

2D-LC/MS/MS analysis was used to examine time-dependent changes in proteome of E. coli O157:H7 strain Sakai upon an abrupt downshift in water activity (aw) (i.e., from aw 0.993 to aw 0.967) at a constant temperature of 35°C. Bacterial cells were harvested before hyperosmotic shift, and 0 (i.e. immediately after the shift), 30, 80, and 310 min after the shift. It also should be noted that these time points were chosen with the aims to characterize the physiology of E. coli during dynamic changes in growth kinetics induced by an abrupt downshift in water activity. Specifically, the samples taken at time 0 and 30 min were obtained during the period in which the loss of cell culturability was observed, whereas the samples at time 80 and 310 min respectively reflected the physiological state of E. coli during the ‘recovery’ period and during growth after the shift.