Objectives: Concentrations of microbial cell wall components such as endotoxin and β-D-glucan in airborne submicrometer particle size fraction (PM1, defined as particles with median aerodynamic diameter, da ≤ 1 μm) have not been well characterized. In this study, airborne concentrations of endotoxin and β-D-glucan among different size fractions were quantified in two distinctly different environments: farms and homes. Effect of microbial source (farm type for farms and mold damage for homes) on size-fractionated concentrations was investigated.
Methods: Airborne endotoxin and β-D-glucan were collected on 7 farms and 184 suburban homes using NIOSH two-stage sampler, a cyclone air sampler that fractionates airborne particles into three size fractions: ≤ 1 μm, 1–1.8 μm and ≥ 1.8 μm.
Results: Geometric means (geometric standard deviations) of airborne total endotoxin concentration on farms and in homes were 1.20 × 104 (7.57) EU/m3 and 2.67 (3.82) EU/m3, respectively. Similar values of airborne total β-D-glucan concentrations were 1.80 × 103 (152.88) ng/m3 and 1.91 (2.83) ng/m3, respectively. Relative proportions of PM1 endotoxin, however, were significantly higher (p < 0.001) in home samples (7.9%) than in farm samples (0.3%). Likewise, the proportion of PM1 β-D-glucan was significantly higher (p < 0.001) in homes (28.2% vs. 2.3%). Farm type significantly influenced concentrations of PM1 β-D-glucan (p < 0.05) and total β-D-glucan (p < 0.001).
Conclusions: The results of this study demonstrate higher proportions of PM1 endotoxin and β-D-glucan in homes compared to farms. These data further emphasize the importance of conducting size-selective air sampling for microbial exposure assessment in homes.