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Abstract
Bacterial killing can be effectively achieved by microwave irradiation; however, it is unclear if non-thermal effects of microwaves are involved in microbial killing. A number of studies have shown that this effect of microwave radiation is solely due to the heat generated during the experimental process, whereas others state that microbial killing could be achieved through nonthermal microwave exposure. In this study, we showed that non-thermal microwave radiation has no significant impact on viability of E. coli C29 bacteria. We also examined the effect of altering membrane composition and fluidity on bacterial resistance to microwave radiation. No change in cell viability was observed upon alteration of membrane composition and fluidity, indicating that they are not significant factors in bacterial resistance to non-thermal microwave radiation. However, our results indicated that membrane fluidity plays an important role in bacterial cell survival during exposure to thermal microwave radiation. We demonstrated that either increasing or decreasing cell membrane fluidity contributed to increased resistance to killing by thermal microwave radiation. The increase in resistance to thermal microwave radiation could also be correlated with decreased permeabilization of cell membrane measured by propidium iodide uptake, suggesting that thermal microwave radiation may inactivate bacteria due to membrane disruption.