title: Growth history influences starvation-induced expression of uspA, grpE, and rpoS and subsequent cryotolerance in Escherichia coli O157:H7.
abstract: In this study, we investigated the effect of starvation on cryotolerance of Escherichia coli O157:H7 grown in tryptic soy broth (TSB) and Luria-Bertani broth (LB). Starved cells (cells suspended in water at 37 degrees C for 6 h) and control cells (cells in TSB or LB) were frozen at -18 degrees C for up to 240 h in their respective growth media. The E. coli grown in TSB showed a greater starvation effect (the difference in percent survival of starved and control cells) and cryotolerance. The starved E. coli grown in TSB showed a 30% increase in their ability to survive frozen storage for 24 h at -18 degrees C. The corresponding increase in survival for LB-grown E. coli was only 3.8%. Cryotolerance induced by starvation of TSB- and LB-grown E. coli was correlated with the expression of genes involved in general stress response pathways, such as uspA, grpE, and rpoS. The expression of uspA, grpE, and rpoS was quantified by measuring the green fluorescence generated from autofluorescent E. coli harboring puspA::gfp, pgrpE::gfp, and prpoS::gfp gene fusions. The results obtained in this study indicate that uspA, grpE, and rpoS were induced on starvation when E. coli was grown in TSB, and their expression correlated well with subsequent induction of cryotolerance developed at -18 degrees C. In contrast, cells grown in LB and subsequently exposed to starvation conditions showed no increase in expression of uspA, grpE, or rpoS, and, as expected, these cells did not exhibit increased cryotolerance at -18 degrees C. Knowledge of molecular mechanisms involved in cross-protection might make it possible to devise strategies to limit their effects and lead to ways to predict the survival of foodborne pathogens in stressful environments.
authors.affiliation: Department of Food Science and Canadian Research Institute for Food Safety, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors.forename: Purushottam V
authors.initials: PV
authors.lastname: Gawande
authors.forename: Mansel W
authors.initials: MW
authors.lastname: Griffiths
mesh_terms: D000222:Adaptation, Physiological; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000235:genetics*; D005453:Fluorescence; D005511:Food Handling / Q000379:methods; D005516:Food Microbiology; D005615:Freezing; D015964:Gene Expression Regulation, Bacterial; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics; D012808:Sigma Factor / Q000096:biosynthesis / Q000235:genetics; D013217:Starvation
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C489400:GrpE protein, E coli; D006360:Heat-Shock Proteins; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; C078564:universal stress protein A, Bacteria