Use of a culture-independent approach to characterize aerosolized bacteria near an open-freestall dairy operation

Authors: Dungan, Robert - Rob

Submitted to: Environment International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2011
Publication Date: 5/1/2012
Citation: Dungan, R.S. 2012. Use of a culture-independent approach to characterize aerosolized bacteria near an open-freestall dairy operation. Environment International. 41(2012):8-14.

Interpretive Summary: Animal manures are known to harbor a variety of pathogens that can potentially be transmitted to humans in the form of airborne particles. In this study, air samples were collected downwind from a 10,000 cow open-freestall dairy and nearby fields being sprinkler irrigated with wastewater. Nucleic acids (DNA) were extracted from the air samples, then a highly conserved gene was sequenced for bacterial identification. Of the 191 gene sequences, none were affiliated with bacteria known to be pathogenic to healthy humans. Our results suggest that there is a low incidence of airborne bacterial pathogens immediately downwind from the dairy and wastewater irrigation sites.

Technical Abstract: Animal manures are known to harbor a variety of zoonotic pathogens, which are suspected of being transported off-site as aerosols from confined feeding operations. In this study, aerosols were collected using a high-volume sampler downwind from a 10,000 cow open-freestall dairy and nearby fields being sprinkler irrigated with wastewater. DNA extracts were prepared from the aerosol samples, then a region of the16S ribosomal RNA gene was sequenced for bacterial identification and phylogenetic classification. At the dairy and irrigation sites, Proteobacteria was the most abundant phylum, representing 78% and 69% of all sequences, respectively, while Actinobacteria, Bacteroidetes and Firmicutes represented only 10% or less of the sequences. Of the 191 clones sequenced from the dairy aerosol samples, 6 sequences were found to be homologous with uncultured bacteria from cow milk, rumen, and fecal samples. However, none of the sequence matches were affiliated with bacteria known to be pathogenic to otherwise healthy humans. Although our results do suggest a high diversity among the aerosolized bacteria, the sampling strategy employed in this study may not account for the variable nature of bioaerosol emissions.