The present study investigated the effects of microwave (MW) radiation applied under a sublethal temperature on Escherichia coli . The experiments were conducted at a frequency of 18 GHz and at a temperature below 40°C to avoid the thermal degradation of bacterial cells during exposure. The absorbed power was calculated to be 1,500 kW/m~(3), and the electric field was determined to be 300 V/m. Both values were theoretically confirmed using CST Microwave Studio 3D Electromagnetic Simulation Software. As a negative control, E. coli cells were also thermally heated to temperatures up to 40°C using Peltier plate heating. Scanning electron microscopy (SEM) analysis performed immediately after MW exposure revealed that the E. coli cells exhibited a cell morphology significantly different from that of the negative controls. This MW effect, however, appeared to be temporary, as following a further 10-min elapsed period, the cell morphology appeared to revert to a state that was identical to that of the untreated controls. Confocal laser scanning microscopy (CLSM) revealed that fluorescein isothiocyanate (FITC)-conjugated dextran (150 kDa) was taken up by the MW-treated cells, suggesting that pores had formed within the cell membrane. Cell viability experiments revealed that the MW treatment was not bactericidal, since 88% of the cells were recovered after radiation. It is proposed that one of the effects of exposing E. coli cells to MW radiation under sublethal temperature conditions is that the cell surface undergoes a modification that is electrokinetic in nature, resulting in a reversible MW-induced poration of the cell membrane.
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机译：本研究调查了亚致死温度下施加的微波（MW）辐射对大肠杆菌的影响。实验是在18 GHz频率和低于40°C的温度下进行的，以避免细菌细胞在暴露过程中发生热降解。计算出吸收功率为1,500 kW / m〜（3），电场为300 V / m。这两个值均使用CST Microwave Studio 3D电磁仿真软件在理论上进行了确认。作为阴性对照，还使用珀耳帖平板加热将大肠杆菌细胞加热到高达40°C的温度。 MW暴露后立即进行的扫描电子显微镜（SEM）分析表明，大肠杆菌细胞表现出与阴性对照明显不同的细胞形态。然而，这种MW作用似乎是暂时的，因为在经过另外10分钟的时间后，细胞形态似乎恢复为与未处理对照相同的状态。共聚焦激光扫描显微镜（CLSM）显示，经MW处理的细胞吸收了异硫氰酸荧光素（FITC）缀合的葡聚糖（150 kDa），表明细胞膜内已形成孔。细胞活力实验表明，MW处理没有杀菌作用，因为88％的细胞在辐射后得以恢复。提出了在亚致死温度条件下将大肠杆菌细胞暴露于MW辐射的作用之一是，细胞表面经历了本质上是电动的修饰，从而导致MW诱导的细胞膜可逆渗透。
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