Evaluation of distinct modes of oxidative secondary injury generated in heat-treated cells of Escherichia coli with solid/liquid and complex/semi-synthetic media sets.

Abstract

To characterize and evaluate oxidative secondary injury generated in heat-treated Escherichia coli cells during recovery cultivation either on agar or in a broth of a semi-synthetic enriched M9 (EM9) medium and a complex Luria broth (LB) medium with different types of antioxidants. E. coli cells grown in the EM9 and LB broth were heated at 50°C in a buffer (pH7.0). Heated cells were recovered on the same kind of agar medium as that used for growth, with or without different antioxidants. Although these antioxidants mostly protected the cells from oxidative secondary injury on the recovery media, sodium thiosulphate and sodium pyruvate were most protective on EM9 and LB agars, respectively. Determination of viability using the most probable number and growth delay analysis methods showed significant reductions in the protective effects of antioxidants in the EM9 and LB media. Oxidative secondary injury generated in heated E. coli cells was found to be qualitatively and quantitatively diverse under cellular and environmental conditions. Our results suggest that different modes of oxidation should be considered in viability determination and injured cell enumeration of heat-treated cells.