Restoration of culturability of starvation-stressed and low-temperature-stressed Escherichia coli O157 cells by using H2O2-degrading compounds

Late-exponential-phase cells of Escherichia coli O157:H- strain E32511/HSC became nonculturable in sterilized distilled water microcosms at 4 degrees C. Plate counts declined from 3 x 10(6) to less than 0.1 CFU/ml in about 21 days. However, when samples of microcosms at 21 days were inoculated onto an agar medium amended with catalase or nonenzyme peroxide-degrading compou nds such as sodium pyruvate or a-ketoglutaric acid, plate counts increased to 10(4)-10(5) CFU/ml within 48 h. The proposed mode of action of the catal ase or pyruvate is via the degradation of the metabolic by-product H2O2, ra ther than through supplementation of a required nutrient in the recovery of nonculturable cells. Our studies were based on the assumption that E32511/ HSC strain responds to starvation and a low temperature by entering a noncu lturable state and that the correction of oxidative stress upon the inocula tion of bacteria on agar plates promotes recovery of nonculturable cells.