Abstract: Objective To evaluate the activity of phospholipase secreted by Cryptococcus neoformans from different sources,serotypes and incubation conditions,and to observe the effect of phospholipase on fungal virulence.Methods The extracelluar phospholpase activity was detected in40isolates of C.neoformans after being incubated onto egg yolk agar.Phospholipase activities of individual isolate were compared according to the ratio of colony diameter to the sum of colony diameter plus precipitation zone(PZ).Infected mouse model was established.The virulence of the isolates was observed based on the colony forming unit(cfu)in cerebral tissue and the survival time of mice infected by C.neoformans with different phospholipase activities.Results Thirty-nine of forty isolates produced distinct precipitation zone on culture media.PZs were 0.529±0.121 and 0.523±0.143 at incubation temperature of 30℃ and 37℃,respectively.Incubated at 37℃,PZs of serotype A,B and AD/D were 0.541±0.116,0.518±0.036 and 0.472±0.051,respectively(P>0.05).PZs of clinical and environmental isolates were 0.501±0.049 and 0.565±0.131,respectively(P<0.05).In vivo,the mean survival time and the cfu in brain were 18.90d,518.67±203.86,in mice infected by C.neoformans with extracellular phospholipase activity and 26.39d,226.47±196.13,respectively,in those without phospholipase activity(P<0.01).Conclusions The incubation temperature has no effect on phospholipase activity.A significant difference of phospholipase activity is found between clinical and environmental isolates,and among isolates of serotype A,B and AD/D.C.neoformans with phospholipase activity exerts stronger virulence in comparison with that without extracelluar phospholipase activity.

Key words: Cryptococcus neoformans, Virulence, Phospholipases