Antibiotic Resistance Genes in Air Near Farms

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

     Abstract Number: 155
     Working Group: Bioaerosols

Abstract
The spread of antimicrobial resistance is considered one of the top 10 global health threats by the World Health Organization. To date most studies on antibiotic resistant genes (ARGs) have focused on water or soil, but ARGs in the air are concerning due to potential long-distance transport. To gain insight into sources of ARG emissions to the atmosphere, we have characterized ARGs in particles collected at two (swine and dairy) farms and wastewater treatment plants. We used a custom-built conditional sampler with a cascade impactor and a viable Andersen impactor to collect particles. At the swine farm, the concentrations of 16S rRNA, representing total bacteria, of ~107 gene copies per cubic meter of air (gc/m3). The number of gene copies decreased with decreasing particle size. Concentrations of the antibiotic resistance gene sul1 totaled ~103 gc/m3, with concentrations decreasing with particle size between 5 microns and 0.5 microns. A substantial amount of sul1 was associated with particles smaller than 0.5 microns, so it is likely part of extracellular DNA. The relative abundance (gene copies per 16S rRNA gene) of sul1 ranged between 7 x 10-5 and 1 x 10-3 gc/16S. We observed culturable E. Coli on all stages larger than 2 microns in the Andersen impactor. Additionally, we saw bacterial growth on all stages with CHROMagar Staph aureus. White, possibly mauve (maybe S. aureus), and light blue colonies appeared on the first three stages (3.3 microns and larger), only white and light blue colonies on the 4th and 5th stages (between 2.1 and 4.7 microns), and 6 white colonies and 1 dark blue colony on the final stage (smaller than 0.65 micron). No resistant bacteria were cultured from any stage of the sampler.