Influence of the current density in moderate pulsed electric fields on P. putida F1 eradication

Eradication of P. putida F1 was investigated as a function of current density in pulsed electric fields of 6.7, 4, 2.8, 2 and 1 kV/cm. The pulse numbers were 200, 2000, 5000 and 10,000 and were performed by a series of trains of 500 pulses (except for the 200 pulses). The frequency was 100 Hz and pulse durations were 10 μs or 20 μs as indicated for each experiment. The current density range was 0.02 ± 0.01 to 5.2 ± 0.5 Acm^-2. A clear tendency for increasing bacterial death was found as a result of increasing the current density in each of the tested electric field strengths. The total bacterial eradication when the electric field was reduced from 4 to 1 kV/cm was obtained at a higher current density, 2 ± 0.2 and 5.2 ± 0.5 Acm^-2, respectively. Increasing the current density led to higher cell permeability and larger bacteria size. The percentage of propidium iodide permeability in an electric field of 1 kV/cm at a current density of 5.2 ± 0.5 Acm^-2 was 65 ± 0.3% compared to the control that was only 10 ± 0.9%. The cell size at 1 kV/cm in a current density of 5.2 ± 0.5 Acm^-2 was about 3-fold higher compared to untreated cells. To the best of our knowledge, this is the first study that evaluated the influence of increasing current density on bacterial eradication in moderate electric fields.