Aerobiology of Yeasts: Viable Colonies and Molecular Identification from Burkard Samples
Saturday, March 5, 2016
South Exhibit Hall H (Convention Center)
Josh D. McLoud, M.S., Estelle Levetin, PhD FAAAAI
Rationale: Various fungal spores are commonly identified microscopically on Burkard air samples; however, yeasts are not identified on these samples.  By contrast, yeast colonies commonly occur on culture-based air samples, but are seldom identified to genus or species.  Since several yeasts are known allergens, their atmospheric concentrations should be elucidated.  The current study was undertaken to develop molecular markers and methods for detecting the presence of yeast in atmospheric samples.

Methods: One-minute air samples for culturable fungi were collected weekly from February through July 2015 with a single-stage Andersen sampler using malt extract agar.  Cultures were identified by microscopy and colony morphology.  Samples for molecular analysis were collected using a Burkard volumetric 7-day spore trap and DNA was extracted from samples on four days.  The molecular analysis included species-specific primers for Aureobasidium pullulans and Saccharomyces cerevisiae along with genus-specific primers for Rhodotorula. DNA was amplified by conventional PCR.

Results: During the 6 months of viable sampling, total yeast concentrations varied from none on 6 February to 954 CFU/m3 on 22 May, when yeasts were 47% of total colonies observed.  Additionally, Rhodotorula accounted for 777 CFU/m3 on May 22.  Molecular markers detected the presence of Rhodotorula on the Burkard samples for all four days tested and Aureobasidium on three of the days.  Saccharomyces cerevisiae was not detected on any of the tested samples.    

Conclusions: This molecular method using conventional PCR can determine the presence and identity of yeasts from Burkard samples.  More work is needed to quantify and determine seasonal trends of these important allergens.