Sensitivity of Candida albicans to negative air ion streams

Negative air ions (NAIs) are known to kill C. albicans; however, their precise mechanism of action is uncertain. Elucidation of this has been hampered by a lack of reproducibility between results obtained by different investigators. The aim of this study was to determine the influence of variation in experimental parameters on the sensitivity of C. albicans to negative air ions and the role of ozone in this process. Ten strains of C. albicans were exposed to NAIs generated at different emitter distances, exposure times, relative humidities and under aerobic and oxygen-free conditions. In further experiments, ozone levels were measured under the same conditions. The effect of NAIs on C. albicans growth was assessed by measuring the area of the zone of inhibition generated around the electrode of the ionizer. There was a significant reduction in area of zone of inhibition with increasing emitter distance (P < 0.05), relative humidity (P < 0.05) or under oxygen-free conditions (P < 0.05). Increases in exposure time resulted in a significant increase in growth inhibition (P < 0.05). Ozone levels increased with increasing exposure times (P < 0.01) but were significantly reduced as emitter distance increased (P < 0.01). When utilized in a nonventilated room, levels of ozone produced did not exceed recognized safety limits. These results (a) demonstrate the importance of careful control of experimental parameters if reproducibility of studies involving NAIs is to be achieved, and (b) highlight the possible role of ozone in the microbicidal effects of NAIs.