Proteomic response of Escherichia coli O157:H7 to simultaneous abrupt downshifts in temperature and water activity

Shiga toxin-producing Escherichia coli (STEC) have emerged as important food-borne pathogens of considerable public health concern. The majority of food-borne outbreaks caused by STEC, particularly serotype O157:H7, appear to be associated with undercooked meat and meat products. Although several intervention strategies are already in use to control carcass contamination, no single intervention is 100% effective in eliminating E. coli from carcasses. This indicates the need for developing effective interventions. Based on observations of E. coli inactivation under combined mild chill and osmotic shocks, as occur during carcass chilling, the Australian meat industry funded this study to investigate air-chilling itself as a potential intervention. A ‘shotgun’ proteomic approach known as multidimensional protein identification technology (‘MudPIT’) was used to characterize time-dependent changes in the proteome of E. coli O157:H7 strain Sakai upon simultaneous rapid downshifts in temperature and water activity (aw), from 35°C aw 0.993 to 14°C aw 0.967. This presentation will discuss proteomic results with emphasis on the stress responses of E. coli. Of particular interest, strain Sakai responded to combined cold osmotic shift by inducing the activity of the RpoE regulon as an emergency response to repair protein misfolding in the cell envelope, and activating the master stress regulator RpoS and the Rcs system-controlled colanic acid biosynthesis to mediate long-term adaptation under the stress condition. The present results will aid the development of more targeted approaches for the meat industry to eliminate or control this pathogen.