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Phospholipase activity in Cryptococcus neoformans: a new virulence factor?
1Centre for Infectious Diseases and Microbiology, University of Sydney, Westmead Hospital, Australia.
Abstract:
Fifty isolates of Cryptococcus neoformans were examined for extracellular phospholipase production after inoculation onto egg yolk agar; 49 produced a pericolonial precipitate indicative of phospholipase activity. Phospholipase B (PLB), lysophospholipase, and lysophospholipase-transacylase activities were identified by radiometric analysis in supernatants from 4 clinical isolates. The ratio of colony diameter to colony plus precipitate on agar (Pz) correlated with PLB activity. Phospholipase production was similar in 12 environmental and 13 clinical isolates of C. neoformans var. gattii. Environmental strains of C. neoformans var. neoformans (n = 8) produced more phospholipase at 72 h than did 17 clinical isolates (mean Pz, 0.57 vs. 0.72; P < .01); however, Pz values were similar at 96 h. Quantitation of cryptococci in the lungs and brains of BALB/c mice inoculated intravenously with 4 strains expressing high, intermediate, or low phospholipase activity revealed a correlation between phospholipase activity and virulence. Phospholipases secreted by C. neoformans may be implicated in virulence.
Insights
Most Cryptococcus neoformans isolates produce phospholipase, an enzyme linked to virulence. Environmental strains of C. neoformans var. neoformans showed higher phospholipase activity than clinical ones, suggesting a role for phospholipase in fungal infections.
Area of Science:
- Mycology
- Pathogenic Microbiology
- Biochemistry
Background:
- Cryptococcus neoformans is an opportunistic fungal pathogen causing cryptococcosis.
- Extracellular phospholipases are virulence factors in various microbial pathogens.
- The role of phospholipase production in C. neoformans virulence is not fully elucidated.
Purpose of the Study:
- To investigate phospholipase production in Cryptococcus neoformans isolates.
- To correlate phospholipase activity with virulence in a murine model.
Main Methods:
- Inoculation of C. neoformans isolates on egg yolk agar to detect phospholipase activity.
- Radiometric analysis of supernatants to quantify specific phospholipase activities (PLB, lysophospholipase, lysophospholipase-transacylase).
- Murine model (BALB/c mice) to assess the correlation between phospholipase activity and fungal burden in organs.
Main Results:
- 49 out of 50 C. neoformans isolates exhibited phospholipase activity.
- Phospholipase B (PLB) activity was confirmed in clinical isolates.
- Environmental C. neoformans var. neoformans strains showed higher phospholipase production at 72 hours compared to clinical isolates.
- A positive correlation was observed between phospholipase activity and fungal load in the lungs and brains of infected mice.
Conclusions:
- Phospholipase production is a common characteristic of C. neoformans.
- Phospholipase activity is associated with the virulence of C. neoformans in a murine model.
- Secreted phospholipases are likely implicated as virulence factors in C. neoformans infections.