Abstract: 【Abstract】 Objective To investigate the effect of 1 064-nm Q-switched Nd:YAG laser at different energy settings on cell viability, protease activity and structures of Malassezia furfur. Methods Cultured standard strains of Malassezia furfur were divided into several groups to be irradiated with 1 064-nm Q-switched Nd:YAG laser at different energies of 0 （control group）, 500, 600, 700, 800 and 900 mJ, respectively. Then, fungal suspensions in the above groups were inoculated onto the Leeming & Notman medium separately. After 7-day culture, the diameter and number of colonies were measured to evaluate the fungal cell viability, the protease activity was measured by using the whole-milk plate medium, and the ultrastructure of Malassezia furfur in each group was observed by transmission electron microscopy. One-way analysis of variance was used for comparisons among multiple groups, least significant difference-t test for multiple comparisons, and Pearson correlation analysis for analyzing correlations of laser energy with colony diameter, colony number and protease activity. Results The colony diameter and number both significantly differed among the control group, 500-, 600-, 700-, 800- and 900-mJ groups （colony diameter: 4.05 ± 0.69, 3.76 ± 0.51, 3.28 ± 0.41, 3.09 ± 0.72, 2.54 ± 0.64 and 2.43 ± 0.41 mm, respectively; colony number: 4 787 ± 597, 4 287 ± 761, 1 879 ± 275, 1 082 ± 248 and 209 ± 42, 72 ± 31 colony-forming units, respectively; F = 14.83, 231.85, respectively, both P < 0.05）, and were significantly lower in the 600-, 700-, 800- and 900-mJ groups than in the control group （all P < 0.05）. The laser energy was negatively correlated with the colony diameter and number （r = -0.67, -0.91, respectively, both P < 0.05）. The protease activity significantly differed among the control group, 500-, 700- and 900-mJ groups （F = 346.60, P < 0.05）, and was significantly lower in the 700- and 900-mJ groups than in the control group （both P < 0.05）. There was a negative correlation between the laser energy and protease activity （r = －0.94, P < 0.05）. Transmission electron microscopy showed intact fungal structures in the control group, relatively intact fungal structures in the 500-mJ group, and obviously damaged fungal structures in the 600- － 900-mJ groups, and the greater the laser energy, the more severely the fungal structures were damaged. Conclusion The 1 064-nm Q-switched Nd:YAG laser could affect the cell viability of and protease activity in Malassezia furfur, and damage the fungal structures.

Key words: Malassezia, Lasers, solid-state, Nd-YAG lasers, Cellular structures, Cell activity, Protease activity