Contribution of dps to acid stress tolerance and oxidative stress tolerance in Escherichia coli O157 : H7

An Escherichia coli O157:H7 dps::nptI mutant (FRIK 47991) was generated, an d its survival was compared to that of the parent in HCl (synthetic gastric fluid, pH 1.8) and hydrogen peroxide (15 mM) challenges. The survival of t he mutant in log phase (5-h culture) was significantly impaired (4-log(10)- CFU/ml reduction) compared to that of the parent strain (ca. 1.0-log(10)-CF U/ml reduction) after a standard 3-h acid challenge. Early-stationary-phase cells (12-h culture) of the mutant decreased by ca. 4 log(10) CFU/ml while the parent strain decreased by approximately 2 log(10) CFU/ml. No signific ant differences in the survival of late-stationary-phase cells (24-h cultur e) between the parent strain and the mutant were observed, although numbers of the parent strain declined less in the initial 1 h of acid challenge. F RIK 47991 was more sensitive to hydrogen peroxide challenge than was the pa rent strain, although survival improved in stationary phase. Complementatio n of the mutant with a functional dps gene restored acid and hydrogen perox ide tolerance to levels equal to or greater than those exhibited by the par ent strain. These results demonstrate that decreases in survival were from the absence of Dps or a protein regulated by Dps. The results from this stu dy establish that Dps contributes to acid tolerance in E. coli O157:H7 and confirm the importance of Dps in oxidative stress protection.