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.
Highlights
The enterohemorrhagic Escherichia coli (EHEC) pathotype is comprised of a diverse group of Shiga toxin-producing E. coli (STEC) strains that cause severe disease, including the potentially fatal haemolytic uremic syndrome (HUS)
The generation times observed at the postdownshift temperature were consistent with the predictive model of Ross et al [45] and the lag time increased with the magnitude of the shift
The relative lag time (RLT) response for E. coli showed no systematic variation across the temperature range tested, indicating that the amount of ‘‘work’’ the population had to perform to adjust to each temperature was similar (Table 2)
Summary
The enterohemorrhagic Escherichia coli (EHEC) pathotype is comprised of a diverse group of Shiga toxin-producing E. coli (STEC) strains that cause severe disease, including the potentially fatal haemolytic uremic syndrome (HUS). E. coli O157:H7 is one of the most important EHEC serotypes in relation to public health, contributing significantly to human infections and outbreaks. The major transmission route for O157:H7 is food-borne, with many different foods and dairy products acting as vectors in outbreaks and sporadic cases of infection [1]. Cattle are the primary reservoir of O157:H7 and this organism can be found in their faeces, rumen, hide, derived carcasses and meat products [2,3,4]. Persistence of this pathogen in the agricultural and food processing industry environments poses potential risks for human health
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