Comparative proteomic analysis of Escherichia coli O157:H7 following ohmic and water bath heating by capillary-HPLC-MS/MS

Escherichia coli O157:H7 is an important food-borne pathogenic microorganism that has been used as a model organism for studying microbial inactivation effects and inactivation mechanism in various sterilization technologies. The objective of this study was to investigate the effects of high voltage short time ohmic- (HVST), low voltage long time ohmic- (LVLT), and water bath- (WB) heating on inactivation and proteome changes of E. coli O157:H7 cells at the same endpoint temperature of 72 °C, and to analyze whether a non-thermal death effect existed in ohmic heating. The inactivation effect of E. coli cells after HVST was comparable to WB, and the largest inactivation was observed after LVLT. There was lower intracellular protein content detected in LVLT and HVST samples than those of WB (P < 0.05). Quantitative proteomic profiles using capillary-HPLC-MS/MS technology identified 2626 proteins, among them, a total of 142 (62 up-regulated and 80 down-regulated), 129 (37 up-regulated and 92 down-regulated), and 61 (20 up-regulated and 41 down-regulated) differential proteins were obtained by comparisons of HVST vs. CT (control), LVLT vs. CT, and WB vs. CT samples, respectively, and revealing a strongest cell response to HVST followed by LVLT and WB. Compared with WB samples, more protein changes in HVST and LVLT samples were mainly attributed to the leakage of intracellular proteins due to the damage of cell membrane by current of ohmic heating. Bioinformatics analysis indicated that the differential proteins were mainly involved in transcription, translation, cell wall and membrane biogenesis, amino acid, carbohydrate, and lipid metabolism. KEGG enrichment analysis indicated that the ribosome, terpenoid backbone biosynthesis, glycerophospholipid metabolism, ABC transporters, and folate biosynthesis were significantly enriched. Overall, the application of both HVST and LVLT treatments had the potential to inactivate E. coli cells, especially HVST with a shorter heating time, and the results in this study presented an important step toward understanding the response of E. coli cells to ohmic heating on proteome level.