Characterization of bioaerosols from dairy barns: reconstructing the puzzle of occupational respiratory diseases by using molecular approaches

Abstract

To understand the etiology of exposure-related diseases and to establish standards for reducing the risks associated with working in contaminated environments, the exact nature of the bioaerosol components must be defined. Molecular biology tools were used to evaluate airborne bacterial and, for the first time, archaeal content of dairy barns. Three air samplers were tested in each of the 13 barns sampled. Up to 10(6) archaeal and 10(8) bacterial 16S rRNA genes per m(3) of air were detected. Archaeal methanogens, mainly Methanobrevibacter species, were represented. Saccharopolyspora rectivirgula, the causative agent of farmer's lung, was quantified to up to 10(7) 16S rRNA genes per m(3) of air. In addition, a wide variety of bacterial agents were present in our air samples within the high airborne bioaerosol concentration range. Despite recommendations regarding hay preservation and baling conditions, farmers still develop an S. rectivirgula-specific humoral immune response, suggesting intense and continuous exposure. Our results demonstrate the complexity of bioaerosol components in dairy barns which could play a role in occupational respiratory diseases.

Fig 1

Airborne archaeal and bacterial 16S rRNA gene concentrations from dairy barn samples (average ± SEM), as determined by quantitative PCR. Comparison between IOM, NIOSH, and Coriolis air samplers (n = 13 each). LOD, 4 × 10² 16S rRNA genes for archaea and 2 × 10³ 16S rRNA genes for bacteria. No statistical differences between results from the three air samplers tested (archaea, P = 0.3135; bacteria, P = 0.4981).

Fig 2

Airborne S. rectivirgula 16S rRNA gene concentrations from dairy barn samples (average ± SEM), as determined by quantitative PCR from the IOM air sampler (n = 13). The dotted line at 2 × 10³ indicates the LOD of the PCR.

Fig 3

Size distribution of particles in the dairy barns: airborne archaeal and bacterial concentrations 16S rRNA gene from dairy barn samples (average ± SEM), as determined by quantitative PCR. Comparison between the three NIOSH sampler stages (n = 13 each). LOD, 1 × 10² 16S rRNA genes for archaea and 6 × 10² 16S rRNA genes for bacteria. *, P < 0.005.

Fig 4

Lack of correlation between the concentrations of 16S rRNA genes of archaea and bacteria in dairy barns. Comparison between IOM (r = 0.2629, P = 0.3853), NIOSH (r = 0.0839, P = 0.7852), and Coriolis (r = 0.0464, P = 0.8803) air samplers (n = 13 each). Data from the same barn are represented by the same color. LOD, 4 × 10² 16S rRNA genes for archaea and 2 × 10³ 16S rRNA genes for bacteria.