Generation of Actinomycetes Aerosols Containing Spores and Mycelium: Performances of a Liquid Bubbling Aerosolizer

The presence of actinomycetes in many workplaces and their role in the incidence of various respiratory symptoms remains poorly understood and underestimated. A sampling and culture-independent analysis method to measure airborne actinomycetes has yet to be developed and controlled bioaerosols are needed for laboratory investigations. In this article, the performances of a single-pass bubbling aerosolizer were characterized to evaluate the feasibility of generating actinomycetes from a liquid source and to confirm that viability of aerosolized entities was preserved. Six preparation protocols for liquid Thermoactinomycetes vulgaris cultures were compared in terms of culturable flora and total spores concentrations (culture and epifluorescence microscopy) and size distributions (optical counter and cascade impactor) of the bioaerosols generated. Using the best protocol, the generator's performances were then validated using three species: Thermoactinomyces vulgaris, Thermobifida fusca, and Streptomyces californicus. Bioaerosols contained a mixture of spores and mycelium and their properties were stable throughout generation (120min) and were satisfactorily reproducible between runs. Depending on the species generated, the culturable concentrations measured were between 10(4) and 10(8) CFU.m(-3), with corresponding total spore concentrations between 10(5) and 10(9) Spores.m(-3). These concentrations cover the ranges measured in the workplace. The generator's flexibility should make it possible to produce bioaerosols with other actinomycetes species, and use them in laboratory trials with various objectives and constraints.