Antibiotic Resistance Genes in Air Near Swine and Dairy Farms

DAVID KORMOS, Gabriel Isaacman-VanWertz, Jactone Ogejo, Amy Pruden, Linsey Marr, Virginia Tech

     Abstract Number: 410
     Working Group: Bioaerosols in Agriculture: Sources, Risks and Mitigation

Abstract
The spread of antimicrobial resistance is a global health threat, and there is an urgent need to identify how it disseminates. To date, most studies on environmental antibiotic resistance genes (ARGs) have focused on water or soil, but airborne ARGs are also important due to their ability to undergo long-distance transport. To gain insight into sources of ARG emissions to the atmosphere from livestock facilities, we characterized ARGs in aerosol particles collected at a swine farm and dairy farm across all seasons. At the swine farm, concentrations of total bacterial markers (16S rRNA genes) and a common anthropogenic indicator ARG (sul1) were significantly elevated at building exhaust vents compared to an upwind location, with differences up to two orders of magnitude. Seasonal variation was evident, with the highest 16S rRNA and sul1 gene concentrations in spring and fall, up to 2x104 gene copies per cubic meter (gc/m³) for sul1. Both genes were predominantly associated with larger particles, with sul1 also found in fine particles (<2.5 µm), indicating potential for long-distance transport. At the dairy farm, where samples were collected at varying distances from an open-air barn, the 16S rRNA gene concentrations were highest in the fall and lowest in the winter. Conversely, sul1 concentrations were highest in the winter. Downwind from the dairy barn, 16S rRNA gene concentrations decreased up to 25 meters away, while sul1 gene concentrations showed no clear downwind pattern in fall and spring, suggesting a link to ambient background levels rather than dominance of the barn as a source. Culturing results showed a higher ratio of antibiotic-resistant to non-resistant colonies at the swine farm in the spring, correlating with increased use of the building’s exhaust fan. Colonies have been preserved for further analysis by whole genome sequencing.