Nitroxyl free radical sensitizers enhance the radiation killing of <tex-math>${\rm K}_{12}\ {\rm RecA}^{-}$</tex-math> bacteria to a greater extent than does oxygen. Unlike oxygen, electron-affinic sensitizers of the nitro-aromatic type cannot compete to reduce this "superoxic" level of sensitization. Instead, the two types of sensitizer, when used in combination, are additive in their effect on reducing the survival of <tex-math>${\rm K}_{12}\ {\rm RecA}^{-}$</tex-math>, suggesting that they operate on different types of radiation-induced lesion. Experiments with other Escherichia coli strains show similar effects.

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