Bacteria of the type E. coli K12 have been treated in experiments using high-voltage pulses of short time (microseconds) as a killing agent. The role of different experimental parameters has been studied: kind of electrolyte, concentration, length of pulses, field strength, pH and temperature. Electrolytes with bivalent cations were found to reduce the lethal action. the relative rate of killed bacteria was shown to be mainly governed by the field strength and the treatment time, which is defined by the product of pulse number and decay time constant. From the obtained results a function has been developed which enables the precalculation of the killing rate for E. coli, provided that certain limits of experimental conditions are considered. No correlation between the applied electric energy and the lethal effect could be found.

Comparative studies were carried out describing the lethal effects of electric pulses on GRAM-negative bacteria, GRAM-positive bacteria, and yeast cells. Microorganisms are killed by the pulse treatment without visible morphological destruction. The observed survival rates are figured as functions of the field strength E and the treatment time t (pulse number X time constant) revealing three explicit parameters as sufficient to explain the kinetics of the results. These parameters are determined by the species of microorganism used and moreover depend on the physiological properties of the microbial population. GRAM-positive bacteria and yeasts were found to be less sensitive to electric pulse treatment than GRAM-negative bacteria, when low pulse numbers are applied. Treatment with high pulse numbers reveals survival rates below 1% for all microorganisms examined. Cells from the logarithmic growth phase are killed in markedly higher percentage than cells harvested from the stationary growth phase. The obtained results as well as further studies confirm the hypothesis of an electric induced selective damage of inner cell membranes.