Toxic Effects upon Bacteria of Phosphate-Buffered Saline Exposed in a High-Frequency Argon Discharge

Abstract

An electrodeless Ar- and H₂-gas discharge apparatus has been used to expose suspensions of E. coli. K-12. H, OH, and e/sub aq/⁻ are formed in the surface layer of the Ar-exposed suspension and attack the cells predominantly from outside. When cells are exposed in the Ar-discharge in phosphate-buffered saline (pH = 6.8), repair-proficient and repair-deficient strains are inactivated with about equal efficiency, with no detectable damage in terms of single-strand breaks either in intracellular phage lambda-DNA or in the bacterial DNA. The lethal effect is shown to be caused almost entirely by an OH- induced toxic product formed from phosphate-buffered saline. The toxic product is not yet identified, but its long lifetime and nonvolatility suggest that it may be an oxidation product of Cl⁻, like HClO. When cells are exposed in the argon discharge setup in phosphate buffer without NaCl, inactivation is negligible. This suggests that the primary action of extracellular OH-radicals is insignificant for the X-ray-induced indirect effect. (auth)