Bacterial decontamination with nanosecond pulsed electric fields

In order to explore the effect of pulsed electric fields (PEF) with pulses, which are of the order of the charging time of bacterial membranes, we have studied the effect of 45 ns pulses on the viability of bacillus subtilis (ATCC6051) in its vegetative state. The treatment chamber consists of two parallel metal plates with the separation of 2.2 mm and an insulating housing, made of PTFE. A 30 Ω Blumlein generator with a low inductance spark gap switch delivers square wave voltage pulses of 45 ns duration to the electrodes of the bacterial treatment chamber. The parameters varied for this study were the resistivity of the medium and the risetime of the pulse. PEF was found to be more effective in media with low resistivity. The risetime, which was varied from 2 ns (f<200 MHz) to 20 ns (f<50 MHz), determines the high frequency components in the Fourier spectrum of the pulse. With pulses of different rise time, but same total energy, the pulse with short rise time kills bacteria more effectively. These results indicate that the high frequency components in PEF deposit the electrical energy in the cell and affect intracellular structures.