Desiccation and Thermal Resistance of Escherichia coli O121 in Wheat Flour

Non-O157 Shiga toxin-producing Escherichia coli infections have recently been associated with wheat flour on two separate accounts in the United States and Canada. However, there is little information regarding the thermal resistance and longevity of non-O157 Shiga toxin-producing Escherichia coli during storage in low-moisture environments. The objectives of this study were to determine the thermal inactivation kinetics of E. coli O121 in wheat flour and to compare the thermal inactivation rates with those of other pathogens. Wheat flour, inoculated with E. coli O121, was equilibrated at 25 degrees C to a water activity of 0.45 in a humidity-controlled conditioning chamber. Inoculated samples were treated isothermally at 70, 75, and 80 degrees C, and posttreatment population survivor ratios were determined by plate counting. D -and z-values calculated with a log-linear model, were compared with those obtained in other studies. At 70, 75, and 808C, the D-values for E. coli O121 were 18.16 +/- 0.96, 6.47 +/- 0.50, and 4.58 +/- 0.40 min, respectively, and the z-value was 14.57 +/- 2.21 degrees C. Overall, E. coli O121 was observed to be slightly less thermally resistant than what has been previously reported for Salmonella Enteritidis PT30 in wheat flour as measured under the same conditions with the same methods.