Bactericidal effects of negative and positive ions generated in nitrogen on Escherichia coli

The bactericidal effect of both negative and positive ions generated by a dc electrical corona in nitrogen were investigated. Tryptic soy broth agar plates inoculated with Escherichia coli (E. coli) (strain DH5-α) were placed into a custom-built multi-point-to-plane ion generator situated within a glass chamber. Under a nitrogen atmosphere the plates were exposed to either negative or positive ions for various time periods. The plates were then removed and incubated at 37°C for 15 h and the colonies counted. Exposure to either negative or positive ions produced significant reductions (p<0.05) in colony number. Bacterial plates exposed to a constant 200 μA negative current for 30 min demonstrated a 65% reduction in colony number compared to unexposed plates. Increasing the exposure current to 400 μA, further increased the level of disinfection at 30 min to 91%. Exposure to 200 μA current of positive ions produced a 72% reduction after 10 min and virtual sterilisation after 30 min with a 98% reduction in colony number. These results indicate that exposure to negative and particularly positive ions has a lethal effect on E. coli cells. Cell death could be due to a physiological change in the outer membrane as a result of ionic interactions.