Redox potential affects the measured heat resistance of Escherichia coli O157:H7 independently of oxygen concentration

Cells of Escherichia coli O157:H7 were heat-treated at 59 °C and enumerated in (i) anaerobic medium with a low redox potential, (ii) anaerobic media with the oxidizing agents potassium ferricyanide or 2,6-dichloroindophenol (DPIP) added to raise the redox potential, (iii) aerobic medium with a high redox potential and (iv) aerobic medium with the reducing agent dithiothreitol added to lower the redox potential. The measured heat-resistance was greatest when the enumeration medium was highly anaerobic due to the absence of oxygen and the presence of hydrogen and cysteine HCl. Measured heat resistance was influenced by the redox potential of the enumeration medium independently of the chemical used to adjust it and therefore, independently of the presence of oxygen. Sub-lethally heat-damaged cells regained their ability to grow in media of high redox potential at a similar rate whether the redox potential was increased by the addition of potassium ferricyanide, DPIP or oxygen.