Identification of high concentrations of an allergenic yeast in the Pasadena aerosol

Abstract

Rationale To identify the type, source and allergenicity of a common particulate bioaerosol collected from the Pasadena air. Methods Air samples were collected with a Burkard spore trap and bioaerosols identified and counted. The morphology of molds isolated from nearby vegetation was examined and compared with the bioaerosols collected from the air. The approximately 600 base-pair D1/D2 region of the large (26S) ribosomal subunit of the isolates was sequenced and compared to published sequences. Skin testing with commercially available extracts was performed to determine the allergenicity of this newly identified bioaerosol. Factors controlling the generation and dispersal of these bioaerosols were evaluated using a controlled emission chamber with an attached aerodynamic particle sizer. Results For the past year we have noticed that yeasts comprise up to 90% (24,000 m-3 of air, 24 hour average) of the total mold counts, especially during moist weather and at night. The flowers of nearby vegetation (e.g. Eucalyptus) were heavily infected with yeasts. The cellular and colonial morphology of yeast isolates was found to be consistent with Aureobasidium. RNA sequence analysis showed identity to two strains of Aureobasidium pullulans. In controlled emission experiments, this yeast readily forms an aerosol of respirable (1–2.5 Î1/4m) particles. Skin test reactivity with A. pullulans revealed approximately 18% of atopic individuals (4/22) positive. Conclusions A. pullulans occurs in high concentrations in the Pasadena air. A. pullulans is a known cause of hypersensitivity pneumonitis. Whether it is relevant as an asthma trigger remains to be determined.