Bactericidal effects of negative and positive ions generated in nitrogen on starved Pseudomonas veronii

Bacterial cells in natural populations are rarely at exponential phase due to insufficient availability of nutrients. Suppression of cell division due to starvation is one of the most common forms of initiating stationary phase. Once initiated, cells at stationary phase are considerably more resistant to a host of challenges. The bactericidal effect on stationary phase cells of both negative or positive ions generated by a d.c. electrical corona in nitrogen was investigated. Bioluminescent Pseudomonas veronii cells, resuspended in sterile water and starved for 24 h, were inoculated onto aluminium foil coupons (2 cm2) and placed into a custom-built multi-point-to-plane ion generator situated within a plastic chamber. Under a nitrogen atmosphere the coupons were exposed to either negative or positive ions for various time periods. Following exposure, cell viability was determined by the measurement of light output recorded from foil coupons using a luminometer and converted to colony forming units per millilitre. Exposure to either negative or positive ions produced significant reductions (p<0.05) in cell viability. These results indicate that exposure to either negative or positive ions has a lethal effect on starved Pseudomonas veronii cells. Cell death could be due to ionic puncturing of the cell wall as a result of ionic accumulation at the outer membrane.