To study the dependence of exposure duration (1 h or 19 h) of continuous wave millimeter wave 99 GHz irradiation on Escherichia coli bacterial cell viability and metabolic activity.
All experiments were performed on Escherichia coli populations during the logarithmic phase. For cell viability tests two exposure methods were used: 1) exposure was conducted on cells that were spread on agar plates, and 2) exposure was conducted on cells that were suspended in two different culture mediums (PBS (to study the cell death) or LB (to study cell division)). For metabolic activity test exposure (19 h) was conducetd on cells that were suspended in LB medium.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
99 GHz
Modulation type:
CW
Exposure duration:
continuous for 1 h
|
|
|
Exposure 2:
99 GHz
Modulation type:
CW
Exposure duration:
continuous 1 h or 19 hr
|
|
| Frequency | 99 GHz |
|---|---|
| Type | |
| Exposure duration | continuous for 1 h |
| Modulation type | CW |
|---|
| Exposure source | |
|---|---|
| Distance between exposed object and exposure source | 22 mm |
| Setup | agar plate at a short distance from the antenna |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| power density | 0.17 mW/cm² | - | calculated | - | at the bacterial plane |
| Frequency | 99 GHz |
|---|---|
| Type | |
| Exposure duration | continuous 1 h or 19 hr |
| Modulation type | CW |
|---|
| Exposure source | |
|---|---|
| Distance between exposed object and exposure source | 0.5 cm |
| Setup | bacterial suspensions placed above the antenna |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| power density | 0.2 mW/cm² | - | calculated | - | at the bacterial plane |
The data showed that 1 hour of exposure to 99 GHz continuous wave electromagnetic field irradiation had no effect on Escherichia coli viability and colony characterisation. In 19 h of exposure, the number of colony forming units was half order of magnitude higher than the sham exposed and the control: In exposed samples, the calculated viable cells in PBS and LB medium were 8.19 x 107 and 1.47 x 109 cells/ml, respectively. In the sham exposed samples, the calculated viable cells in PBS and LB medium were 3.47 x 107 and 8.41 x 108 cells/ml, respectively. However, 19 h of exposure did not affect the metabolic activity.
The authors conclude that exposure of Escherichia coli to millimeter wave 99 GHz irradiation (continuous wave) for a short period did not affect the viability of Escherichia 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, the authors assume that the slight proliferation (half order of magnitude) after 19 h of exposure does not have a biological meaning.
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