Submicronic fungal bioaerosols: high-resolution microscopic characterization and quantification

Area of Science:

• Environmental Science
• Microbiology
• Aerosol Science

Background:

• Submicronic particles from fungal cultures are potential sources of personal exposure in mold-contaminated environments.
• Previous methods for identifying fungal particles relied on size and autofluorescence, with limited confirmation of fungal origin.
• The generation and characteristics of submicronic fungal particles remain incompletely understood.

Purpose of the Study:

• To investigate and quantify the in vitro release of submicronic fungal particles from specific fungal species.
• To compare the efficacy of a novel bioaerosol generator and a fungal spores source strength tester.
• To confirm the fungal origin of submicronic particles and identify their sources (hyphae, conidia).

Main Methods:

• Aerosolization of submicronic particles from Aspergillus fumigatus, Aspergillus versicolor, and Penicillium chrysogenum cultures grown on agar and gypsum board.
• Enumeration of particles using field emission scanning electron microscopy (FESEM).
• Comparison of two aerosolization devices at different airflow rates (12 and 20 L/min).

Main Results:

• Aspergillus fumigatus released significantly higher median numbers of submicronic particles (2 × 10^5 cm⁻²) compared to A. versicolor (2.6 × 10³ cm⁻²) and P. chrysogenum (0.9 × 10³ cm⁻²).
• The ratios of submicronic fragments to larger particles varied among species (1:3 for A. fumigatus, 5:1 for A. versicolor, 1:2 for P. chrysogenum).
• Spore fragments with rodlets constituted 13% of submicronic particles from A. fumigatus, 2% from A. versicolor, and 0% from P. chrysogenum.

Conclusions:

• Both hyphae and conidia can fragment into submicronic particles and become aerosolized in vitro.
• Fungal fragments, particularly from A. fumigatus, significantly contribute to the aerosolized submicronic particle load.
• These findings underscore the importance of considering fungal fragments in assessing personal fungal exposure in indoor environments.