Mode of bacterial inactivation by chlorine dioxide

This study was conducted to examine the effects of chlorine dioxide on dehydrogenase enzymes, protein synthesis, and deoxyribonucleic acid of bacteria in order to elucidate the mode of action of chlorine dioxide. Experiments were carried out in a specially designed unit which permitted sampling for bacterial survivals at time intervals from 5 to 1800 s after the addition of the disinfectant. Bacterial numbers were determined by the pour plate technique. The total dehydrogenase activity of Escherichia coli was determined by the colorimetric estimation of triphenyl formazan, and cell extracts were assayed for their ability to incorporate radioactive phenylalanine into protein. DNA extracted from chlorine dioxide-treated Haemophilus influenzae was tested for its ability to transform competent cells. Partially purified DNA was also exposed to chlorine dioxide and tested for transformability.Experimental results show that total dehydrogenase enzymes were completely inhibited within the first 5 s of reaction even while considerable numbers of bacteria remained viable. Protein synthesis was partially inhibited by chlorine dioxide and the extent of inhibition was found to be proportional to the initial chlorine dioxide dosage. Glutathione did not reverse the effect of chlorine dioxide on bacterial viability, total dehydrogenase activity or protein synthesis. When whole cells of H. influenzae were exposed to chlorine dioxide, the DNA transforming activity was not affected. Similarly, when a partially purified extract of H. influenzae DNA was treated with chlorine dioxide, no inhibition of DNA transformation occurred within the first minute of reaction. Moreover, after a contact time of 5 min or more, a very high chlorine dioxide dose of 20 mg l⁻¹ produced only a slight inhibition of DNA transforming function. Thus, the primary site of action of chlorine dioxide on bacteria must lie elsewhere in the cell other than in the dehydrogenase enzymes, the protein synthesizing complex or DNA, although inhibition of protein synthesis may have a contributory lethal effect.