Evaluation of non-thermal effect of microwave radiation and its mode of action in bacterial cell inactivation

Abstract

A growing body of literature has recognized the non-thermal effect of pulsed microwave radiation (PMR) on bacterial systems. However, its mode of action in deactivating bacteria has not yet been extensively investigated. Nevertheless, it is highly important to advance the applications of PMR from simple to complex biological systems. In this study, we first optimized the conditions of the PMR device and we assessed the results by simulations, using ANSYS HFSS (High Frequency Structure Simulator) and a 3D particle-in-cell code for the electron behavior, to provide a better overview of the bacterial cell exposure to microwave radiation. To determine the sensitivity of PMR, Escherichia coli and Staphylococcus aureus cultures were exposed to PMR (pulse duration: 60 ns, peak frequency: 3.5 GHz) with power density of 17 kW/cm2 at the free space of sample position, which would induce electric field of 8.0 kV/cm inside the PBS solution of falcon tube in this experiment at 25 °C. At various discharges (D) of microwaves, the colony forming unit curves were analyzed. The highest ratios of viable count reductions were observed when the doses were increased from 20D to 80D, which resulted in an approximate 6 log reduction in E. coli and 4 log reduction in S. aureus. Moreover, scanning electron microscopy also revealed surface damage in both bacterial strains after PMR exposure. The bacterial inactivation was attributed to the deactivation of oxidation-regulating genes and DNA damage.

Low-Temperature Plasma for Biology, Hygiene, and Medicine: Perspective and Roadmap

“…In vivo, necrosis may trigger an immune response or an inflammatory response [235], where physical factors in LTP are very relevant in direct treatment strategies. Furthermore, based on the results of a recent study, the effects of MW emission from a plasma were determined to have decontamination efficacy [236]. This transbarrier capacity of LTP treatment suggests the noninvasive potential in medical application but more extensive studies are needed to understand the mechanism of interaction of physically based modalities with cells and tissues.…”

Study and application status of the nonthermal effects of microwaves in chemistry and materials science – a brief review

“…The application of MWs in cell inactivation also reflected the theory of the interaction of electric fields with specific molecules. Priyanka Shaw et al 47 found in a study of the inactivation of bacterial cells by MW irradiation that MWs can interact with molecules on the surfaces of bacterial cells, thereby causing changes in cell morphology and further leading to failure of the intracellular oxidative defence machinery and DNA damage-mediated inactivation of bacterial cells.…”

Microwaves, a potential treatment for bacteria: A review

“…However, their ability to eliminate bacterial infections has not received enough attention. MW as a component of the electromagnetic spectrum, are non-ionizing radiation with frequencies ranging from 300 MHz to 300 GHz, and wavelengths between 1 m and 1 mm ( Mawioo et al, 2016 ; Wang et al, 2019a ; Shaw et al, 2021 ). The effects of MW include thermal and non-thermal ( Rougier et al, 2014 ; Shaw et al, 2021 ), and it is generally believed that the temperature increase caused by MW exposure plays a key role in microorganism inactivation ( Rougier et al, 2014 ; Shaw et al, 2021 ).…”

“…MW as a component of the electromagnetic spectrum, are non-ionizing radiation with frequencies ranging from 300 MHz to 300 GHz, and wavelengths between 1 m and 1 mm ( Mawioo et al, 2016 ; Wang et al, 2019a ; Shaw et al, 2021 ). The effects of MW include thermal and non-thermal ( Rougier et al, 2014 ; Shaw et al, 2021 ), and it is generally believed that the temperature increase caused by MW exposure plays a key role in microorganism inactivation ( Rougier et al, 2014 ; Shaw et al, 2021 ). The MW-based thermal effect is different from conventional heating ( Shaw et al, 2021 ), involving the dielectric properties of polar substance molecules, which have a shorter heating time than conventional heating.…”

“…The effects of MW include thermal and non-thermal ( Rougier et al, 2014 ; Shaw et al, 2021 ), and it is generally believed that the temperature increase caused by MW exposure plays a key role in microorganism inactivation ( Rougier et al, 2014 ; Shaw et al, 2021 ). The MW-based thermal effect is different from conventional heating ( Shaw et al, 2021 ), involving the dielectric properties of polar substance molecules, which have a shorter heating time than conventional heating. More importantly, MW-based non-thermal effects can destroy microorganisms at temperatures below the thermal destruction point, which can disrupt cell membranes and increase the amount of DNA and proteins released from cells ( Woo et al, 2000 ; Shaw et al, 2021 ).…”