Effect of nutrient starvation on the resistance of Escherichia coli O157 :H7 to subsequent heat stress

The resistance of three strains of Escherichia coli O157:H7 in their statio nary growth phase to starvation (24 h in water at 37 degreesC) followed by a heat treatment (56 degreesC for up to 90 min) was determined. Starvation was found to increase significantly the resistance of two strains (NCTC 120 79; eae(+), VT1(+), VT2(+), and ATCC 43889 eae(+), VT2(+)) but not the rema ining strain (ATCC 43890 eae(+), VT1(+)). Strain NCTC 12079 (only one teste d) was shown to retain all of the three virulence factors after the two str esses. De novo protein synthesis was shown to be required for heat resistan ce. Evidence using an rpoS mutant indicated a central role for this gene in inducing heat resistance after a starvation stress. It is hoped that this work will contribute to more accurate risk assessments in certain food proc essing operations.