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Aims:  To clarify the effects of O− (atomic oxygen radical anion) water on the viability and morphological alteration of Escherichia coli. Methods and Results:  O− water (OW) was prepared by bubbling of O−/argon (Ar) flux into deionized water. O− and hydrogen peroxide (H2O2) in the resultant OW were analysed by electron paramagnetic resonance and ultraviolet (UV) absorption spectroscopy. The population of E. coli treated by a typical OW of pH 4·30 ± 0·20 [(2·5 ± 0·8) × 10−3 mmol l−1 O−; 0·5 ± 0·2 mmol l−1 H2O2) was reduced by more than 3 log CFU ml−1 within 60 min at 30°C. Through scanning electron microscopy observation, the OW‐treated cells appeared dramatically collapsed. The release of nucleic acid induced by OW was identified by UV absorption spectroscopy. Conclusions:  O− water can result in inactivation of E. coli, nucleic acid release and cellular damage under the controlled laboratory conditions in excess of 15–30 min. Reactive oxygen species may play an important role in the inactivation process. Significance and Impact of the Study:  This study first revealed that OW could inactivate E. coli, which may be potentially useful in developing a novel approach for the microbial decontamination of food, water or heat‐sensitive material.

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