Global Genome Response of Escherichia coli O157∶H7 Sakai during Dynamic Changes in Growth Kinetics Induced by an Abrupt Temperature Downshift

Abstract

Escherichia coli O157∶H7 is a mesophilic food-borne pathogen. We investigated the growth kinetics of E. coli O157∶H7 Sakai during an abrupt temperature downshift from 35°C to either 20°C, 17°C, 14°C or 10°C; as well as the molecular mechanisms enabling growth after cold stress upon an abrupt downshift from 35°C to 14°C in an integrated transcriptomic and proteomic analysis. All downshifts caused a lag period of growth before growth resumed at a rate typical of the post-shift temperature. Lag and generation time increased with the magnitude of the shift or with the final temperature, while relative lag time displayed little variation across the test range. Analysis of time-dependent molecular changes revealed, in keeping with a decreased growth rate at lower temperature, repression of genes and proteins involved in DNA replication, protein synthesis and carbohydrate catabolism. Consistent with cold-induced remodelling of the bacterial cell envelope, alterations occurred in the expression of genes and proteins involved in transport and binding. The RpoS regulon exhibited sustained induction confirming its importance in adaptation and growth at 14°C. The RpoE regulon was transiently induced, indicating a potential role for this extracytoplasmic stress response system in the early phase of low temperature adaptation during lag phase. Interestingly, genes previously reported to be amongst the most highly up-regulated under oxidative stress were consistently down-regulated. This comprehensive analysis provides insight into the molecular mechanisms operating during adaptation of E. coli to growth at low temperature and is relevant to its physiological state during chilling in foods, such as carcasses.

Physiological Response of Escherichia coli O157:H7 Sakai to Dynamic Changes in Temperature and Water Activity as Experienced during Carcass Chilling

“…The strain of E. coli O157:H7 Sakai (19, 20) used in this study was provided by Carlton Gyles (Guelph, Canada). A stock culture was maintained at −80 °C and was cultivated by plating onto brain-heart infusion (BHI) agar (Thermo Scientific, Waltham, MA, CM225) and incubating at 37 °C for 24 h. An isolated colony was inoculated into 25 ml of BHI broth and incubated at 37 °C for 20 h. The resulting broth culture was kept at 4 °C and used as a “working” culture within a week.…”

“…The T-profiler t test based method of Boorsma et al (33) was performed on the log 2 expression ratios, as previously described (19, 20), to determine changes in overall expression of a predefined set of proteins cold osmotic shock.…”

“…This study was extended to investigate the growth kinetics of this pathogen subjected to an abrupt downshift in water activity (a w 0.993 to either a w 0.980, 0.975, 0.970, 0.967, or 0.960) (19) and temperature (35 °C to either 20 °C, 17 °C, 14 °C or 10 °C) (20), as well as to examine the time-dependent alterations in its transcriptome and proteome during adaptation upon an abrupt downshift in a w (from 0.993 to a w 0.967 (19)) and temperature (from 35 °C to 14 °C (20)). In combination these studies revealed that E. coli O157:H7 appeared to lose, and then recover, culturability because of the effects of an abrupt downshift in a w ; but not in temperature.…”

“…The genome-wide expression response of E. coli was analyzed by both cDNA microarray (transcriptome response) and 2D-LC/MS/MS analysis (proteome response) as previously described (18–20), to characterize the potential mechanisms enabling this pathogen to adapt and/or survive under combined stresses.…”

Combined effect of chilling and desiccation on survival of Escherichia coli suggests a transient loss of culturability

“…This suggests a "window" of cell susceptibility in which novel "intervention" strategies might be applied to more successfully reduce E. coli levels on carcasses. Reinforcing these observations, King et al (2014) and Kocharunchitt et al (2014) used an integrated transcriptomic and proteomic approach to study the physiological response of E. coli to a rapid downshift in temperature or water activity, respectively. Those studies showed distinct proteomic and transcriptomic responses of E. coli to abrupt temperature or water activity shifts, and identified potential susceptibilities to oxidative stress of E. coli during exposure to combined chilling and osmotic stress conditions.…”