Effect of 99GHz continuous millimeter wave electro-magnetic radiation on E. coli viability and metabolic activity

Purpose:To investigate time exposure dependence of continuous millimeter wave (CW) 99GHz radiation on Escherichia coli bacterial cell viability and metabolic activity. Materials and methods:Suspensions of E. coli bacterial cells with an optical density of OD660nm0.1 were used for viability tests and OD660nm1.0 for metabolic activity tests. These suspensions were exposed to 99GHz CW electromagnetic radiation, generated by a Backward Wave Oscillator (BWO) tube base instrument with a horn antenna at the BWO exit, to obtain an almost ideal Gaussian beam. Calculations of the Gaussian beam show that a power of 0.2mW/cm² was obtained at the bacterial plane. Results:The experimental results show that 1 hour of exposure to 99GHz CW electromagnetic radiation had no effect on E. coli viability and colony characterisation. In 19h of radiation, the number of colonies forming units was half order of magnitude higher than the sham-exposed and the control. However, 19h of exposure did not affect the E. coli metabolic activity. Conclusions:Exposure of E. coli to millimeter wave (MW) CW 99GHz radiation for a short period did not affect the viability of E. coli bacterial cells. However, exposure for 19h caused a slight proliferation but did not influence the metabolic activities of about 90 biochemical reactions that were examined. Hence, we assume that the slight proliferation (half order of magnitude) after 19h of exposure dose not have a biological meaning.