Sensitivity of Candida albicans to negative air ion streams

Negative air ions (NAIs) are known to kill C. albicans; however, their prec ise mechanism of action is uncertain. Elucidation of this has been hampered by a lack of reproducibility between results obtained by different investi gators. The aim of this study was to determine the influence of variation i n 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 wer e exposed to NAIs generated at different emitter distances, exposure times, relative humidities and under aerobic and oxygen-free conditions. In furth er experiments, ozone levels were measured under the same conditions. The e ffect of NAIs on C. albicans growth was assessed by measuring the area of t he zone of inhibition generated around the electrode of the ionizer. There was a significant reduction in area of zone of inhibition with increasing e mitter distance (P < 0.05), relative humidity (P < 0.05) or under oxygen-fr ee conditions(P < 0.05). Increases in exposure time resulted in a significa nt increase in growth inhibition (P < 0.05). Ozone levels increased with in creasing exposure times (P < 0.01) but were significantly reduced as emitte r distance increased (P < 0.01). When utilized in a nonventilated room, lev els of ozone produced did not exceed recognized safety limits. These result s (a) demonstrate the importance of careful control of experimental paramet ers if reproducibility of studies involving NAIs is to be achieved, and (b) highlight the possible role of ozone in the microbicidal effects of NAIs.