Factors affecting the surviving fractions of resting Escherichia coli B and K-12 cells exposed to alternating current.

Resting Escherichia coli B and K-12 cells suspended in a phosphate buffer solution were exposed to alternating current (AC) of 50 Hz.The surviving fractions of cells exposed to ACwere decreased with an increase in current density from 0 to 300mA/cm2at 29±3°C for a definite exposure time.At a definite current density the fractions were decreased proportionally with exposure time.Even for conditions of definite exposure time and current density, the fractions varied depending on the concentration of cells initially suspended in buffer solution in AC-exposure chamber.E. coli cells weremoreresistant to AC-exposureunder anaerobic conditions than aerobic conditions.Addition of catalase to the cell suspension during AC-exposure effectively protected both strains.Methionine and albumin had mild protective effects, but chemicals, such as cysteine, ehanol or a-tocopherol had little protective effect.The passage of low-frequency alternating current (AC) through a cell suspension at nonlethal temperature has been knownto exert a killing effect, and this action was found to be primarily due to toxic substances formed in the suspension by electrolysis.1~4)Fritz,1}using Ag-metal electrodes, believed that silver salts and free chlorine generated by electrolytic action of ACwere responsible for the killing effects on yeast cells.Tracy2) proposed that the formation of temporary toxic substances, like free chlorine might cause the killing effect.Recently, using certain group of VIII transition metal electrodes, Rosenberg et al?) demonstrated that metal complexes, e.g.Pt (IV) complexes, or ions like Ni2+ produced in the medium at the level of about 1~10 ppm by electrolysis, caused inhibition of Escherichia coli cell division or resulted in bacterial death.