EFFECT OF MILLIMETER WAVES ON SURVIVAL OF UVC-EXPOSED ESCHERICHIA-COLI

Bacterial cells of the strain Escherichia coli K12 were exposed to mil limeter electromagnetic waves (mm waves) with and without additional e xposure to ultraviolet light lambda = 254 nm (UVC). The mm waves were produced by a medical microwave generator emitting a 4-GHz-wide band a round a 61 GHz center frequency and delivering an irradiation of 1 mW/ cm(2) and a standard absorption rate (SAR) of 84 W/kg to the bacteria. Exposure to the mm waves alone for up to 30 minutes did not change th e survival rate of bacteria. Exposure to mm waves followed by WC irrad iation also did not alter the number of surviving E. coli cells in com parison to UVC-treated controls. When mm waves were applied after the WC exposure, a dose-dependent increase of up to 30% in the survival of E. coli was observed compared to UVC + sham-irradiated bacteria. Beca use sham controls and experimental samples were maintained under the s ame thermal conditions, the effect is not likely to be due to heating, although the possibility of nonuniform distribution of microwave heat ing in different layers of irradiated bacterial suspension cannot be r uled out. The mechanism for this effect appears to involve certain DNA repair systems that act as cellular targets for mm waves. (C) 1995 Wi ley-Liss, Inc.