Abstract
BackgroundIn recent years there has been renewed interest in the use of air ionisers to control of the spread of airborne infection. One characteristic of air ions which has been widely reported is their apparent biocidal action. However, whilst the body of evidence suggests a biocidal effect in the presence of air ions the physical and biological mechanisms involved remain unclear. In particular, it is not clear which of several possible mechanisms of electrical origin (i.e. the action of the ions, the production of ozone, or the action of the electric field) are responsible for cell death. A study was therefore undertaken to clarify this issue and to determine the physical mechanisms associated with microbial cell death.ResultsIn the study seven bacterial species (Staphylococcus aureus, Mycobacterium parafortuitum, Pseudomonas aeruginosa, Acinetobacter baumanii, Burkholderia cenocepacia, Bacillus subtilis and Serratia marcescens) were exposed to both positive and negative ions in the presence of air. In order to distinguish between effects arising from: (i) the action of the air ions; (ii) the action of the electric field, and (iii) the action of ozone, two interventions were made. The first intervention involved placing a thin mica sheet between the ionisation source and the bacteria, directly over the agar plates. This intervention, while leaving the electric field unaltered, prevented the air ions from reaching the microbial samples. In addition, the mica plate prevented ozone produced from reaching the bacteria. The second intervention involved placing an earthed wire mesh directly above the agar plates. This prevented both the electric field and the air ions from impacting on the bacteria, while allowing any ozone present to reach the agar plate. With the exception of Mycobacterium parafortuitum, the principal cause of cell death amongst the bacteria studied was exposure to ozone, with electroporation playing a secondary role. However in the case of Mycobacterium parafortuitum, electroporation resulting from exposure to the electric field appears to have been the principal cause of cell inactivation.ConclusionThe results of the study suggest that the bactericidal action attributed to negative air ions by previous researchers may have been overestimated.
Highlights
In recent years there has been renewed interest in the use of air ionisers to control the spread of airborne infection
Results from a clinical trial in an intensive care unit suggest that negative air ions may have the potential to control some hospital acquired infections (HAIs) [1]
Various researchers have reported that 'air' ions inhibit the growth of Penicillium notatum [2,3], Neurospora crassa [3], Serratia marcescens [4], "Staphylococcus albus" [5], Candida albicans [6], Escherichia coli [7], Pseudomonas veronii [8], Aspergillus versicolor [9], Enterococcus malodoratus [9], Staphylococcus chromogenes [9] and Sarcina flava [9]
Summary
In recent years there has been renewed interest in the use of air ionisers to control of the spread of airborne infection. Various researchers have reported that 'air' ions inhibit the growth of Penicillium notatum [2,3], Neurospora crassa [3], Serratia marcescens [4], "Staphylococcus albus" [5], Candida albicans [6], Escherichia coli [7], Pseudomonas veronii [8], Aspergillus versicolor [9], Enterococcus malodoratus [9], Staphylococcus chromogenes [9] and Sarcina flava [9]. While this body of work collectively suggests a biocidal effect in the presence of ions, in both air [2-7,9] and nitrogen [7,8], the physical and biological mechanisms involved remain unclear. In this study seven bacterial species were exposed to both positive and negative ions in the presence of air for various durations and the bactericidal effects recorded
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