Non-Thermal Lethal Effects of Low-Voltage Alternating Current on Bacillus cereus

The bactericidal mechanisms of low-voltage alternating current (0-300 mA cm super(-2)) on the bacteria B. cereus were investigated. The B. cereus cells in logarithmic phase suspended in phosphate buffer solution (0.2 M) were exposed to alternating current of 50 Hz, 120 V under aerobic conditions. The related parameters for bactericidal actions by low-voltage alternating current were measured. At the temperature 29 plus or minus 3 degree C (non-lethal temperature), the surviving fractions of cells exposed to Alternating Current (AC) were decreased with an increase in current density for a definite exposure time. At a certain current density, the surviving fractions were decreased proportionally with exposure time. The lethal effect to cells was attributed to the toxicity of hydrogen peroxide and direct effect of alternating current. These surviving fractions were closely related to the amount of H sub(2)O sub(2) formed in the cell suspensions. At a definite current density, the amount of H sub(2)O sub(2) in the suspension increased with increasing AC-exposure time. At a definite exposure time, the amount of H sub(2)O sub(2) increased with increasing current density. The H sub(2)O sub(2) was produced on the surface of carbon electrodes by AC-electrolytic reduction of dissolved oxygen. The suitable condition for efficient bactericidal by low-voltage AC at non-lethal temperature was AC-exposure at 300 mA cm super(-2) for 1 h or 200 mA cm super(-2) for 3 h. This study shows that the low-voltage alternating current method is a promising technology for the nonthermal pasteurization of foods and is an appropriate complement or replacement of traditional thermal. Furthermore, the mechanism of bactericidal activity by AC may offer a useful method for eradicating bacteria from catheter surfaces.