Fungal fragments as indoor air biocontaminants

Abstract

The aerosolization process of fungal propagules of three species (Aspergillus versicolor, Penicillium melinii, and Cladosporium cladosporioides) was studied by using a newly designed and constructed aerosolization chamber. We discovered that fungal fragments are aerosolized simultaneously with spores from contaminated agar and ceiling tile surfaces. Concentration measurements with an optical particle counter showed that the fragments are released in higher numbers (up to 320 times) than the spores. The release of fungal propagules varied depending on the fungal species, the air velocity above the contaminated surface, and the texture and vibration of the contaminated material. In contrast to spores, the release of fragments from smooth surfaces was not affected by air velocity, indicating a different release mechanism. Correlation analysis showed that the number of released fragments cannot be predicted on the basis of the number of spores. Enzyme-linked immunosorbent assays with monoclonal antibodies produced against Aspergillus and Penicillium fungal species showed that fragments and spores share common antigens, which not only confirmed the fungal origin of the fragments but also established their potential biological relevance. The considerable immunological reactivity, the high number, and the small particle size of the fungal fragments may contribute to human health effects that have been detected in buildings with mold problems but had no scientific explanation until now. This study suggests that future fungal spore investigations in buildings with mold problems should include the quantitation of fungal fragments.

FIG. 1.

Experimental setup (A) and its modification for testing the immunological reactivity of fungal propagules (B).

FIG. 2.

Optical size distribution of A. versicolor, C. cladosporioides, and P. melinii propagules released from both agar and ceiling tile surfaces (composite values) during 30-min experiments.

FIG. 3.

SEM pictures of propagules released from a ceiling tile contaminated with A. versicolor (panel A, intact spores; panel B, fragments).

FIG. 4.

Number of fungal fragments and spores released simultaneously from agar surfaces at four different air velocities during 30-min experiments. The error bars indicate the standard deviation of 6 repeats for A. versicolor, 4 repeats for C. cladosporioides, and 10 repeats for P. melinii. The spore data are taken from Górny et al. (18).

FIG. 5.

ELISA reactivity (defined as optical density) of fungal fragments and spores with three MAbs: MAb 14F7, MAb 5F7, and MAb 12G2. The error bars indicate the standard deviation of three repeats.