Variation in resistance to high hydrostatic pressure and rpoS heterogeneity in natural isolates of Escherichia coli O157 : H7

Several natural isolates of Escherichia coli O157:H7 have previously been s hown to exhibit stationary-phase-dependent variation in their resistance to inactivation by high hydrostatic pressure. In this report we demonstrate t hat loss of the stationary-phase-inducible sigma factor RpoS resulted in de creased resistance to pressure in E. coli O157:H7 and in a commensal strain . Furthermore, variation in the RpoS activity of the natural isolates of O1 57:H7 correlated with the pressure resistance of those strains. Heterogenei ty was noted in the rpoS alleles of the natural isolates that may explain t he differences in RpoS activity. These results are consistent with a role f or rpoS in mediating resistance to high hydrostatic pressure in E. coli O15 7:H7.