Probing bactericidal mechanisms induced by cold atmospheric plasmas with <i>Escherichia coli</i> mutants

Mechanisms of plasma-induced microbial inactivation have commonly been studied with physicochemical techniques. In this letter, Escherichia coli K-12 and its ΔrecA, ΔrpoS, and ΔsoxS mutants are employed to discriminate effects of UV photons, OH radicals, and reactive oxygen species produced in atmospheric discharges. This microbiological approach exploits the fact that these E. coli mutants are defective in their resistance against various external stresses. By interplaying bacterial inactivation kinetics with optical emission spectroscopy, oxygen atoms are identified as a major contributor in plasma inactivation with minor contributions from UV photons, OH radicals, singlet oxygen metastables, and nitric oxide.