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

Purpose:?To investigate time exposure dependence of continuous millimeter wave (CW) 99?GHz radiation on Escherichia coli bacterial cell viability and metabolic activity.

Materials and methods:?Suspensions of E. coli bacterial cells with an optical density of OD_660nm?=?0.1 were used for viability tests and OD_660nm?=?1.0 for metabolic activity tests. These suspensions were exposed to 99?GHz 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 0.2?mW/cm² was obtained at the bacterial plane.

Results:?The experimental results show that 1 hour of exposure to 99?GHz CW electromagnetic radiation had no effect on E. coli viability and colony characterisation. In 19?h of radiation, the number of colonies forming units was half order of magnitude higher than the sham-exposed and the control. However, 19?h of exposure did not affect the E. coli metabolic activity.

Conclusions:?Exposure of E. coli to millimeter wave (MW) CW 99?GHz radiation for a short period did not affect the viability of E. coli bacterial cells. However, exposure for 19?h 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 19?h of exposure dose not have a biological meaning.