Electrostatic bacterial control

Abstract

The following work describes the bacterial effect of either negative or positive ions, generated by an electrical corona discharge in nitrogen.  Bacterial samples were selected for the study to represent both Gram-negative and Gram-positive species, and naturally occurring resistant phenotypes that exist in everyday environmental conditions.  These were Escherichia coli, Staphylococcus aureus, starved Pseudomonas veronii cells or Pseudomonas veronii biofilms.  Samples were placed into a custom-built multi-point-to-plane ion generator, situated within a sealed chamber.  Under a nitrogen atmosphere, to prevent ozone formation, microbial samples were exposed to either negative or positive ions for various time periods and corona current levels.  The results from this study have demonstrated an antibacterial effect of both negative and positive unipolar ions, with significant reductions (up to two log) in bacterial numbers for all the target samples.  Of the two polarities, positive ions were significantly more effective than negative at reducing microbial load, with a mean kill rate of 72% compared to 50% for negative.  This could possibly be due to the net negative surface charge that exists on the cell walls of both Gram-negative and Gram-positive bacteria.

Gram-negative bacteria have been shown to be more susceptible to ionic challenge than Gram-positive, with S. aureus achieving higher viability results after treatment, compared to both E. coli and P. veronii.  This is possibly due to the lower peptidoglycan content in their cell walls.  As to a mechanism for microbial death, this is possibly due to the Mendis et al cell wall disruption model (2001), which is proposed to function by accumulation of charge at the outer membrane surface.  The attractive force that exists between oppositely charged groups on either side of the cell wall cause it to narrow and eventually collapse.

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