Effect of two aerosolization methods on the release of fungal propagules from a contaminated agar surface

Abstract

The effect of perpendicular and swirling aerozolization methods on the release of fungal fragments and spores from agar surface was studied. Three fungal species (Aspergillus versicolor, Cladosporium cladosporioides, Penicillium chrysogenum) were selected for the tests as they commonly occur indoors, create different hyphae structure when they grow on surfaces, and have different spore shapes, aerodynamic sizes, and formation mechanisms. As the tested surface, Petri dishes filled with malt extract agar, separately inoculated with fungal strains and cultivated to obtain an abundant and even growth were used. For the purpose of these experiments, a new aerosolization chamber was built in which HEPA-filtered air stream responsible for fungal propagule release was either perpendicularly directed towards the contaminated surface or set in swirling motion above it. The experiments were conducted at 2 air velocities, typical for outdoor environment (11.6 m/s) and ventilation ducts (29.1 m/s). Concentrations and size distributions of released fragments and spores were measured using an optical particle counter. The results showed that the propagule release depends on the direction (swirling motion was able to release up to 3.4 × 10(5) fragments and 3 × 10(5) spores from 1 cm( 2) of contaminated surface, i.e. significantly more than the perpendicularly directed air stream), velocity (the higher the swirling air velocity applied, the higher the number of released propagules) of the air stream above the contaminated surface, and varied due to the taxonomical species origin (the higher number of particulates was released by Aspergillus colonies). Hence, the efficient control of both microbial fragments and spores, not only in the air, but also in their source should be an integral part of the quality control procedure.