Lethal effects of high-intensity violet 405-nm light on Saccharomyces cerevisiae, Candida albicans, and on dormant and germinating spores of Aspergillus niger

Abstract This study assessed the effects of high-intensity violet light on selected yeast and mould fungi. Cell suspensions of Saccharomyces cerevisiae , Candida albicans , and dormant and germinating spores (conidia) of the mould Aspergillus niger were exposed to high-intensity narrow band violet light with peak output at 405 nm generated from a light-emitting diode (LED) array. All three fungal species were inactivated by the 405-nm light without a requirement for addition of exogenous photosensitiser chemicals. Of the fungal species tested, S. cerevisiae was most sensitive and dormant conidia of A. niger were most resistant to 405-nm light exposure. Five-log 10 colony forming units per millilitre (CFU ml −1 ) reductions of the tested species required exposure doses of 288 J cm −2 for S. cerevisiae , 576 J cm −2 for C. albicans , and a much higher value of 2.3 kJ cm −2 for dormant conidia of A. niger . During germination, A. niger conidia became more sensitive to 405-nm light exposure and sensitivity increased as germination progressed over an 8 h test period. Light exposure under aerobic and anaerobic conditions, together with results obtained using ascorbic acid as a scavenger of reactive oxygen species, revealed that 405-nm light inactivation in fungi involved an oxygen-dependent mechanism, as previously described in bacteria. The inactivation results achieved with yeast cells and fungal spores together with operational advantages associated with the use of a visible (nonultraviolet (UV)) light source highlight the potential of 405-nm light for fungal decontamination applications.